Tag Archives: Machine Translation

Unsupervised speech-to-speech translation from monolingual data

Posted by Eliya Nachmani, Research Scientist, and Michelle Tadmor Ramanovich, Software Engineer, Google Research

Speech-to-speech translation (S2ST) is a type of machine translation that converts spoken language from one language to another. This technology has the potential to break down language barriers and facilitate communication between people from different cultures and backgrounds.

Previously, we introduced Translatotron 1 and Translatotron 2, the first ever models that were able to directly translate speech between two languages. However they were trained in supervised settings with parallel speech data. The scarcity of parallel speech data is a major challenge in this field, so much that most public datasets are semi- or fully-synthesized from text. This adds additional hurdles to learning translation and reconstruction of speech attributes that are not represented in the text and are thus not reflected in the synthesized training data.

Here we present Translatotron 3, a novel unsupervised speech-to-speech translation architecture. In Translatotron 3, we show that it is possible to learn a speech-to-speech translation task from monolingual data alone. This method opens the door not only to translation between more language pairs but also towards translation of the non-textual speech attributes such as pauses, speaking rates, and speaker identity. Our method does not include any direct supervision to target languages and therefore we believe it is the right direction for paralinguistic characteristics (e.g., such as tone, emotion) of the source speech to be preserved across translation. To enable speech-to-speech translation, we use back-translation, which is a technique from unsupervised machine translation (UMT) where a synthetic translation of the source language is used to translate texts without bilingual text datasets. Experimental results in speech-to-speech translation tasks between Spanish and English show that Translatotron 3 outperforms a baseline cascade system.

Translatotron 3

Translatotron 3 addresses the problem of unsupervised S2ST, which can eliminate the requirement for bilingual speech datasets. To do this, Translatotron 3’s design incorporates three key aspects:

Pre-training the entire model as a masked autoencoder with SpecAugment, a simple data augmentation method for speech recognition that operates on the logarithmic mel spectogram of the input audio (instead of the raw audio itself) and is shown to effectively improve the generalization capabilities of the encoder.
Unsupervised embedding mapping based on multilingual unsupervised embeddings (MUSE), which is trained on unpaired languages but allows the model to learn an embedding space that is shared between the source and target languages.
A reconstruction loss based on back-translation, to train an encoder-decoder direct S2ST model in a fully unsupervised manner.

The model is trained using a combination of the unsupervised MUSE embedding loss, reconstruction loss, and S2S back-translation loss. During inference, the shared encoder is utilized to encode the input into a multilingual embedding space, which is subsequently decoded by the target language decoder.

Architecture

Translatotron 3 employs a shared encoder to encode both the source and target languages. The decoder is composed of a linguistic decoder, an acoustic synthesizer (responsible for acoustic generation of the translation speech), and a singular attention module, like Translatotron 2. However, for Translatotron 3 there are two decoders, one for the source language and another for the target language. During training, we use monolingual speech-text datasets (i.e., these data are made up of speech-text pairs; they are not translations).

Encoder

The encoder has the same architecture as the speech encoder in the Translatotron 2. The output of the encoder is split into two parts: the first part incorporates semantic information whereas the second part incorporates acoustic information. By using the MUSE loss, the first half of the output is trained to be the MUSE embeddings of the text of the input speech spectrogram. The latter half is updated without the MUSE loss. It is important to note that the same encoder is shared between source and target languages. Furthermore, the MUSE embedding is multilingual in nature. As a result, the encoder is able to learn a multilingual embedding space across source and target languages. This allows a more efficient and effective encoding of the input, as the encoder is able to encode speech from both languages into a common embedding space, rather than maintaining a separate embedding space for each language.

Decoder

Like Translatotron 2, the decoder is composed of three distinct components, namely the linguistic decoder, the acoustic synthesizer, and the attention module. To effectively handle the different properties of the source and target languages, however, Translatotron 3 has two separate decoders, for the source and target languages.

Two part training

The training methodology consists of two parts: (1) auto-encoding with reconstruction and (2) a back-translation term. In the first part, the network is trained to auto-encode the input to a multilingual embedding space using the MUSE loss and the reconstruction loss. This phase aims to ensure that the network generates meaningful multilingual representations. In the second part, the network is further trained to translate the input spectrogram by utilizing the back-translation loss. To mitigate the issue of catastrophic forgetting and enforcing the latent space to be multilingual, the MUSE loss and the reconstruction loss are also applied in this second part of training. To ensure that the encoder learns meaningful properties of the input, rather than simply reconstructing the input, we apply SpecAugment to encoder input at both phases. It has been shown to effectively improve the generalization capabilities of the encoder by augmenting the input data.

Training objective

During the back-translation training phase (illustrated in the section below), the network is trained to translate the input spectrogram to the target language and then back to the source language. The goal of back-translation is to enforce the latent space to be multilingual. To achieve this, the following losses are applied:

MUSE loss: The MUSE loss measures the similarity between the multilingual embedding of the input spectrogram and the multilingual embedding of the back-translated spectrogram.
Reconstruction loss: The reconstruction loss measures the similarity between the input spectrogram and the back-translated spectrogram.

In addition to these losses, SpecAugment is applied to the encoder input at both phases. Before the back-translation training phase, the network is trained to auto-encode the input to a multilingual embedding space using the MUSE loss and reconstruction loss.

MUSE loss

To ensure that the encoder generates multilingual representations that are meaningful for both decoders, we employ a MUSE loss during training. The MUSE loss forces the encoder to generate such a representation by using pre-trained MUSE embeddings. During the training process, given an input text transcript, we extract the corresponding MUSE embeddings from the embeddings of the input language. The error between MUSE embeddings and the output vectors of the encoder is then minimized. Note that the encoder is indifferent to the language of the input during inference due to the multilingual nature of the embeddings.

The training and inference in Translatotron 3. Training includes the reconstruction loss via the auto-encoding path and employs the reconstruction loss via back-translation.

Audio samples

Following are examples of direct speech-to-speech translation from Translatotron 3:

Spanish-to-English (on Conversational dataset)

Input (Spanish)
TTS-synthesized reference (English)
Translatotron 3 (English)

Spanish-to-English (on CommonVoice11 Synthesized dataset)

Input (Spanish)
TTS-synthesized reference (English)
Translatotron 3 (English)

Spanish-to-English (on CommonVoice11 dataset)

Input (Spanish)
TTS reference (English)
Translatotron 3 (English)

Performance

To empirically evaluate the performance of the proposed approach, we conducted experiments on English and Spanish using various datasets, including the Common Voice 11 dataset, as well as two synthesized datasets derived from the Conversational and Common Voice 11 datasets.

The translation quality was measured by BLEU (higher is better) on ASR (automatic speech recognition) transcriptions from the translated speech, compared to the corresponding reference translation text. Whereas, the speech quality is measured by the MOS score (higher is better). Furthermore, the speaker similarity is measured by the average cosine similarity (higher is better).

Because Translatotron 3 is an unsupervised method, as a baseline we used a cascaded S2ST system that is combined from ASR, unsupervised machine translation (UMT), and TTS (text-to-speech). Specifically, we employ UMT that uses the nearest neighbor in the embedding space in order to create the translation.

Translatotron 3 outperforms the baseline by large margins in every aspect we measured: translation quality, speaker similarity, and speech quality. It particularly excelled on the conversational corpus. Moreover, Translatotron 3 achieves speech naturalness similar to that of the ground truth audio samples (measured by MOS, higher is better).

Translation quality (measured by BLEU, where higher is better) evaluated on three Spanish-English corpora.

Speech similarity (measured by average cosine similarity between input speaker and output speaker, where higher is better) evaluated on three Spanish-English corpora.

Mean-opinion-score (measured by average MOS metric, where higher is better) evaluated on three Spanish-English corpora.

Future work

As future work, we would like to extend the work to more languages and investigate whether zero-shot S2ST can be applied with the back-translation technique. We would also like to examine the use of back-translation with different types of speech data, such as noisy speech and low-resource languages.

Acknowledgments

The direct contributors to this work include Eliya Nachmani, Alon Levkovitch, Yifan Ding, Chulayutsh Asawaroengchai, Heiga Zhen, and Michelle Tadmor Ramanovich. We also thank Yu Zhang, Yuma Koizumi, Soroosh Mariooryad, RJ Skerry-Ryan, Neil Zeghidour, Christian Frank, Marco Tagliasacchi, Nadav Bar, Benny Schlesinger and Yonghui Wu.

Source: Google AI Blog

FRMT: A Benchmark for Few-Shot Region-Aware Machine Translation

Posted by Parker Riley, Software Engineer, and Jan Botha, Research Scientist, Google Research

Many languages spoken worldwide cover numerous regional varieties (sometimes called dialects), such as Brazilian and European Portuguese or Mainland and Taiwan Mandarin Chinese. Although such varieties are often mutually intelligible to their speakers, there are still important differences. For example, the Brazilian Portuguese word for “bus” is ônibus, while the European Portuguese word is autocarro. Yet, today’s machine translation (MT) systems typically do not allow users to specify which variety of a language to translate into. This may lead to confusion if the system outputs the “wrong” variety or mixes varieties in an unnatural way. Also, region-unaware MT systems tend to favor whichever variety has more data available online, which disproportionately affects speakers of under-resourced language varieties.

In “FRMT: A Benchmark for Few-Shot Region-Aware Machine Translation”, accepted for publication in Transactions of the Association for Computational Linguistics, we present an evaluation dataset used to measure MT systems’ ability to support regional varieties through a case study on Brazilian vs. European Portuguese and Mainland vs. Taiwan Mandarin Chinese. With the release of the FRMT data and accompanying evaluation code, we hope to inspire and enable the research community to discover new ways of creating MT systems that are applicable to the large number of regional language varieties spoken worldwide.

Challenge: Few-Shot Generalization

Most modern MT systems are trained on millions or billions of example translations, such as an English input sentence and its corresponding Portuguese translation. However, the vast majority of available training data doesn’t specify what regional variety the translation is in. In light of this data scarcity, we position FRMT as a benchmark for few-shot translation, measuring an MT model’s ability to translate into regional varieties when given no more than 100 labeled examples of each language variety. MT models need to use the linguistic patterns showcased in the small number of labeled examples (called “exemplars”) to identify similar patterns in their unlabeled training examples. In this way, models can generalize, producing correct translations of phenomena not explicitly shown in the exemplars.

An illustration of a few-shot MT system translating the English sentence, “The bus arrived,” into two regional varieties of Portuguese: Brazilian (🇧🇷; left) and European (🇵🇹; right).

Few-shot approaches to MT are attractive because they make it much easier to add support for additional regional varieties to an existing system. While our work is specific to regional varieties of two languages, we anticipate that methods that perform well will be readily applicable to other languages and regional varieties. In principle, those methods should also work for other language distinctions, such as formality and style.

Data Collection

The FRMT dataset consists of partial English Wikipedia articles, sourced from the Wiki40b dataset, that have been translated by paid, professional translators into different regional varieties of Portuguese and Mandarin. In order to highlight key region-aware translation challenges, we designed the dataset using three content buckets: (1) Lexical, (2) Entity, and (3) Random.

The Lexical bucket focuses on regional differences in word choice, such as the "ônibus" vs. "autocarro” distinction when translating a sentence with the word “bus” into Brazilian vs. European Portuguese, respectively. We manually collected 20-30 terms that have regionally distinctive translations according to blogs and educational websites, and filtered and vetted the translations with feedback from volunteer native speakers from each region. Given the resulting list of English terms, we extracted texts of up to 100 sentences each from the associated English Wikipedia articles (e.g., bus). The same process was carried out independently for Mandarin.
The Entity bucket is populated in a similar way and concerns people, locations or other entities strongly associated with one of the two regions in question for a given language. Consider an illustrative sentence like, “In Lisbon, I often took the bus.” In order to translate this correctly into Brazilian Portuguese, a model must overcome two potential pitfalls:
1. The strong geographical association between Lisbon and Portugal might influence a model to generate a European Portuguese translation instead, e.g., by selecting "autocarro” rather than "ônibus".
2. Replacing “Lisbon” with “Brasília” might be a naive way for a model to localize its output toward Brazilian Portuguese, but would be semantically inaccurate, even in an otherwise fluent translation.
The Random bucket is used to check that a model correctly handles other diverse phenomena, and consists of text from 100 randomly sampled articles from Wikipedia’s “featured” and “good” collections.

Evaluation Methodology

To verify that the translations collected for the FRMT dataset capture region-specific phenomena, we conducted a human evaluation of their quality. Expert annotators from each region used the Multi-dimensional Quality Metrics (MQM) framework to identify and categorize errors in the translations. The framework includes a category-wise weighting scheme to convert the identified errors into a single score that roughly represents the number of major errors per sentence; so a lower number indicates a better translation. For each region, we asked MQM raters to score both translations from their region and translations from their language’s other region. For example, Brazilian Portuguese raters scored both the Brazilian and European Portuguese translations. The difference between these two scores indicates the prevalence of linguistic phenomena that are acceptable in one variety but not the other. We found that in both Portuguese and Chinese, raters identified, on average, approximately two more major errors per sentence in the mismatched translations than in the matched ones. This indicates that our dataset truly does capture region-specific phenomena.

While human evaluation is the best way to be sure of model quality, it is often slow and expensive. We therefore wanted to find an existing automatic metric that researchers can use to evaluate their models on our benchmark, and considered chrF, BLEU, and BLEURT. Using the translations from a few baseline models that were also evaluated by our MQM raters, we discovered that BLEURT has the best correlation with human judgments, and that the strength of that correlation (0.65 Pearson correlation coefficient, ρ) is comparable to the inter-annotator consistency (0.70 intraclass correlation).

Metric			Pearson's ρ
chrF			0.48
BLEU			0.58
BLEURT			0.65

Correlation between different automatic metrics and human judgements of translation quality on a subset of FRMT. Values are between -1 and 1; higher is better.

System Performance

Our evaluation covered a handful of recent models capable of few-shot control. Based on human evaluation with MQM, the baseline methods all showed some ability to localize their output for Portuguese, but for Mandarin, they mostly failed to use knowledge of the targeted region to produce superior Mainland or Taiwan translations.

Google’s recent language model, PaLM, was rated best overall among the baselines we evaluated. In order to produce region-targeted translations with PaLM, we feed an instructive prompt into the model and then generate text from it to fill in the blank (see the example shown below).

    Translate the following texts from English to European Portuguese.
    English: [English example 1].
    European Portuguese: [correct translation 1].
    ...
    English: [input].
    European Portuguese: _____"

PaLM obtained strong results using a single example, and had marginal quality gains on Portuguese when increasing to ten examples. This performance is impressive when taking into consideration that PaLM was trained in an unsupervised way. Our results also suggest language models like PaLM may be particularly adept at memorizing region-specific word choices required for fluent translation. However, there is still a significant performance gap between PaLM and human performance. See our paper for more details.

MQM performance across dataset buckets using human and PaLM translations. Thick bars represent the region-matched case, where raters from each region evaluate translations targeted at their own region. Thin, inset bars represent the region-mismatched case, where raters from each region evaluate translations targeted at the other region. Human translations exhibit regional phenomena in all cases. PaLM translations do so for all Portuguese buckets and the Mandarin lexical bucket only.

Conclusion

In the near future, we hope to see a world where language generation systems, especially machine translation, can support all speaker communities. We want to meet users where they are, generating language fluent and appropriate for their locale or region. To that end, we have released the FRMT dataset and benchmark, enabling researchers to easily compare performance for region-aware MT models. Validated via our thorough human-evaluation studies, the language varieties in FRMT have significant differences that outputs from region-aware MT models should reflect. We are excited to see how researchers utilize this benchmark in development of new MT models that better support under-represented language varieties and all speaker communities, leading to improved equitability in natural-language technologies.

Acknowledgements

We gratefully acknowledge our paper co-authors for all their contributions to this project: Timothy Dozat, Xavier Garcia, Dan Garrette, Jason Riesa, Orhan Firat, and Noah Constant. For helpful discussion and comments on the paper, we thank Jacob Eisenstein, Noah Fiedel, Macduff Hughes and Mingfei Lau. For essential feedback around specific regional language differences, we thank Andre Araujo, Chung-Ching Chang, Andreia Cunha, Filipe Gonçalves, Nuno Guerreiro, Mandy Guo, Luis Miranda, Vitor Rodrigues and Linting Xue. For logistical support in collecting human translations and ratings, we thank the Google Translate team. We thank the professional translators and MQM raters for their role in producing the dataset. We also thank Tom Small for providing the animation in this post.

Source: Google AI Blog

Unlocking Zero-Resource Machine Translation to Support New Languages in Google Translate

Posted by Isaac Caswell and Ankur Bapna, Research Scientists, Google Translate

Machine translation (MT) technology has made significant advances in recent years, as deep learning has been integrated with natural language processing (NLP). Performance on research benchmarks like WMT have soared, and translation services have improved in quality and expanded to include new languages. Nevertheless, while existing translation services cover languages spoken by the majority of people world wide, they only include around 100 languages in total, just over 1% of those actively spoken globally. Moreover, the languages that are currently represented are overwhelmingly European, largely overlooking regions of high linguistic diversity, like Africa and the Americas.

There are two key bottlenecks towards building functioning translation models for the long tail of languages. The first arises from data scarcity; digitized data for many languages is limited and can be difficult to find on the web due to quality issues with Language Identification (LangID) models. The second challenge arises from modeling limitations. MT models usually train on large amounts of parallel (translated) text, but without such data, models must learn to translate from limited amounts of monolingual text, which is a novel area of research. Both of these challenges need to be addressed for translation models to reach sufficient quality.

In “Building Machine Translation Systems for the Next Thousand Languages”, we describe how to build high-quality monolingual datasets for over a thousand languages that do not have translation datasets available and demonstrate how one can use monolingual data alone to train MT models. As part of this effort, we are expanding Google Translate to include 24 under-resourced languages. For these languages, we created monolingual datasets by developing and using specialized neural language identification models combined with novel filtering approaches. The techniques we introduce supplement massively multilingual models with a self supervised task to enable zero-resource translation. Finally, we highlight how native speakers have helped us realize this accomplishment.

Meet the Data
Automatically gathering usable textual data for under-resourced languages is much more difficult than it may seem. Tasks like LangID, which work well for high-resource languages, are unsuccessful for under-resourced languages, and many publicly available datasets crawled from the web often contain more noise than usable data for the languages they attempt to support. In our early attempts to identify under-resourced languages on the web by training a standard Compact Language Detector v3 (CLD3) LangID model, we too found that the dataset was too noisy to be usable.

As an alternative, we trained a Transformer-based, semi-supervised LangID model on over 1000 languages. This model supplements the LangID task with the MAsked Sequence-to-Sequence (MASS) task to better generalize over noisy web data. MASS simply garbles the input by randomly removing sequences of tokens from it, and trains the model to predict these sequences. We applied the Transformer-based model to a dataset that had been filtered with a CLD3 model and trained to recognize clusters of similar languages.

We then applied the open sourced Term Frequency-Inverse Internet Frequency (TF-IIF) filtering to the resulting dataset to find and discard sentences that were actually in related high-resource languages, and developed a variety of language-specific filters to eliminate specific pathologies. The result of this effort was a dataset with monolingual text in over 1000 languages, of which 400 had over 100,000 sentences. We performed human evaluations on samples of 68 of these languages and found that the majority (>70%) reflected high-quality, in-language content.

The amount of monolingual data per language versus the amount of parallel (translated) data per language. A small number of languages have large amounts of parallel data, but there is a long tail of languages with only monolingual data.

Meet the Models
Once we had a dataset of monolingual text in over 1000 languages, we then developed a simple yet practical approach for zero-resource translation, i.e., translation for languages with no in-language parallel text and no language-specific translation examples. Rather than limiting our model to an artificial scenario with only monolingual text, we also include all available parallel text data with millions of examples for higher resource languages to enable the model to learn the translation task. Simultaneously, we train the model to learn representations of under-resourced languages directly from monolingual text using the MASS task. In order to solve this task, the model is forced to develop a sophisticated representation of the language in question, developing a complex understanding of how words relate to other words in a sentence.

Relying on the benefits of transfer learning in massively multilingual models, we train a single giant translation model on all available data for over 1000 languages. The model trains on monolingual text for all 1138 languages and on parallel text for a subset of 112 of the higher-resourced languages.

At training time, any input the model sees has a special token indicating which language the output should be in, exactly like the standard formulation for multilingual translation. Our additional innovation is to use the same special tokens for both the monolingual MASS task and the translation task. Therefore, the token translate_to_french may indicate that the source is in English and needs to be translated to French (the translation task), or it may mean that the source is in garbled French and needs to be translated to fluent French (the MASS task). By using the same tags for both tasks, a translate_to_french tag takes on the meaning, “Produce a fluent output in French that is semantically close to the input,” regardless of whether the input is garbled in the same language or in another language entirely. From the model’s perspective, there is not much difference between the two.

Surprisingly, this simple procedure produces high quality zero-shot translations. The BLEU and ChrF scores for the resulting model are in the 10–40 and 20–60 ranges respectively, indicating mid- to high-quality translation. We observed meaningful translations even for highly inflected languages like Quechua and Kalaallisut, despite these languages being linguistically dissimilar to all other languages in the model. However, we only computed these metrics on the small subset of languages with human-translated evaluation sets. In order to understand the quality of translation for the remaining languages, we developed an evaluation metric based on round-trip translation, which allowed us to see that several hundred languages are reaching high translation quality.

To further improve quality, we use the model to generate large amounts of synthetic parallel data, filter the data based on round-trip translation (comparing a sentence translated into another language and back again), and continue training the model on this filtered synthetic data via back-translation and self-training. Finally, we fine-tune the model on a smaller subset of 30 languages and distill it into a model small enough to be served.

Translation accuracy scores for 638 of the languages supported in our model, using the metric we developed (RTTLangIDChrF), for both the higher-resource supervised languages and the low-resource zero-resource languages.

Contributions from Native Speakers
Regular communication with native speakers of these languages was critical for our research. We collaborated with over 100 people at Google and other institutions who spoke these languages. Some volunteers helped develop specialized filters to remove out-of-language content overlooked by automatic methods, for instance Hindi mixed with Sanskrit. Others helped with transliterating between different scripts used by the languages, for instance between Meetei Mayek and Bengali, for which sufficient tools didn’t exist; and yet others helped with a gamut of tasks related to evaluation. Native speakers were also key for advising in matters of political sensitivity, like the appropriate name for the language, and the appropriate writing system to use for it. And only native speakers could answer the ultimate question: given the current quality of translation, would it be valuable to the community for Google Translate to support this language?

Closing Notes
This advance is an exciting first step toward supporting more language technologies in under-resourced languages. Most importantly, we want to stress that the quality of translations produced by these models still lags far behind that of the higher-resource languages supported by Google Translate. These models are certainly a useful first tool for understanding content in under-resourced languages, but they will make mistakes and exhibit their own biases. As with any ML-driven tool, one should consider the output carefully.

The complete list of new languages added to Google Translate in this update:

Acknowledgements
We would like to thank Julia Kreutzer, Orhan Firat, Daan van Esch, Aditya Siddhant, Mengmeng Niu, Pallavi Baljekar, Xavier Garcia, Wolfgang Macherey, Theresa Breiner, Vera Axelrod, Jason Riesa, Yuan Cao, Mia Xu Chen, Klaus Macherey, Maxim Krikun, Pidong Wang, Alexander Gutkin, Apurva Shah, Yanping Huang, Zhifeng Chen, Yonghui Wu, and Macduff Hughes for their contributions to the research, engineering, and leadership of this project.

We would also like to extend our deepest gratitude to the following native speakers and members of affected communities, who helped us in a wide variety of ways: Yasser Salah Eddine Bouchareb (Algerian Arabic); Mfoniso Ukwak (Anaang); Bhaskar Borthakur, Kishor Barman, Rasika Saikia, Suraj Bharech (Assamese); Ruben Hilare Quispe (Aymara); Devina Suyanto (Balinese); Allahserix Auguste Tapo, Bakary Diarrassouba, Maimouna Siby (Bambara); Mohammad Jahangir (Baluchi); Subhajit Naskar (Bengali); Animesh Pathak, Ankur Bapna, Anup Mohan, Chaitanya Joshi, Chandan Dubey, Kapil Kumar, Manish Katiyar, Mayank Srivastava, Neeharika, Saumya Pathak, Tanya Sinha, Vikas Singh (Bhojpuri); Bowen Liang, Ellie Chio, Eric Dong, Frank Tang, Jeff Pitman, John Wong, Kenneth Chang, Manish Goregaokar, Mingfei Lau, Ryan Li, Yiwen Luo (Cantonese); Monang Setyawan (Caribbean Javanese); Craig Cornelius (Cherokee); Anton Prokopyev (Chuvash); Rajat Dogra, Sid Dogra (Dogri); Mohamed Kamagate (Dyula); Chris Assigbe, Dan Ameme, Emeafa Doe, Irene Nyavor, Thierry Gnanih, Yvonne Dumor (Ewe); Abdoulaye Barry, Adama Diallo, Fauzia van der Leeuw, Ibrahima Barry (Fulfulde); Isabel Papadimitriou (Greek); Alex Rudnick (Guarani); Mohammad Khdeir (Gulf Arabic); Paul Remollata (Hiligaynon); Ankur Bapna (Hindi); Mfoniso Ukwak (Ibibio); Nze Lawson (Igbo); D.J. Abuy, Miami Cabansay (Ilocano); Archana Koul, Shashwat Razdan, Sujeet Akula (Kashmiri); Jatin Kulkarni, Salil Rajadhyaksha, Sanjeet Hegde Desai, Sharayu Shenoy, Shashank Shanbhag, Shashi Shenoy (Konkani); Ryan Michael, Terrence Taylor (Krio); Bokan Jaff, Medya Ghazizadeh, Roshna Omer Abdulrahman, Saman Vaisipour, Sarchia Khursheed (Kurdish (Sorani));Suphian Tweel (Libyan Arabic); Doudou Kisabaka (Lingala); Colleen Mallahan, John Quinn (Luganda); Cynthia Mboli (Luyia); Abhishek Kumar, Neeraj Mishra, Priyaranjan Jha, Saket Kumar, Snehal Bhilare (Maithili); Lisa Wang (Mandarin Chinese); Cibu Johny (Malayalam); Viresh Ratnakar (Marathi); Abhi Sanoujam, Gautam Thockchom, Pritam Pebam, Sam Chaomai, Shangkar Mayanglambam, Thangjam Hindustani Devi (Meiteilon (Manipuri)); Hala Ajil (Mesopotamian Arabic); Hamdanil Rasyid (Minangkabau); Elizabeth John, Remi Ralte, S Lallienkawl Gangte,Vaiphei Thatsing, Vanlalzami Vanlalzami (Mizo); George Ouais (MSA); Ahmed Kachkach, Hanaa El Azizi (Morrocan Arabic); Ujjwal Rajbhandari (Newari); Ebuka Ufere, Gabriel Fynecontry, Onome Ofoman, Titi Akinsanmi (Nigerian Pidgin); Marwa Khost Jarkas (North Levantine Arabic); Abduselam Shaltu, Ace Patterson, Adel Kassem, Mo Ali, Yonas Hambissa (Oromo); Helvia Taina, Marisol Necochea (Quechua); AbdelKarim Mardini (Saidi Arabic); Ishank Saxena, Manasa Harish, Manish Godara, Mayank Agrawal, Nitin Kashyap, Ranjani Padmanabhan, Ruchi Lohani, Shilpa Jindal, Shreevatsa Rajagopalan, Vaibhav Agarwal, Vinod Krishnan (Sanskrit); Nabil Shahid (Saraiki); Ayanda Mnyakeni (Sesotho, Sepedi); Landis Baker (Seychellois Creole); Taps Matangira (Shona); Ashraf Elsharif (Sudanese Arabic); Sakhile Dlamini (Swati); Hakim Sidahmed (Tamazight); Melvin Johnson (Tamil); Sneha Kudugunta (Telugu); Alexander Tekle, Bserat Ghebremicael, Nami Russom, Naud Ghebre (Tigrinya); Abigail Annkah, Diana Akron, Maame Ofori, Monica Opoku-Geren, Seth Duodu-baah, Yvonne Dumor (Twi); Ousmane Loum (Wolof); and Daniel Virtheim (Yiddish).

Source: Google AI Blog

Introducing CVSS: A Massively Multilingual Speech-to-Speech Translation Corpus

Posted by Ye Jia and Michelle Tadmor Ramanovich, Software Engineers, Google Research

Automatic translation of speech from one language to speech in another language, called speech-to-speech translation (S2ST), is important for breaking down the communication barriers between people speaking different languages. Conventionally, automatic S2ST systems are built with a cascade of automatic speech recognition (ASR), text-to-text machine translation (MT), and text-to-speech (TTS) synthesis sub-systems, so that the system overall is text-centric. Recently, work on S2ST that doesn’t rely on intermediate text representation is emerging, such as end-to-end direct S2ST (e.g., Translatotron) and cascade S2ST based on learned discrete representations of speech (e.g., Tjandra et al.). While early versions of such direct S2ST systems obtained lower translation quality compared to cascade S2ST models, they are gaining traction as they have the potential both to reduce translation latency and compounding errors, and to better preserve paralinguistic and non-linguistic information from the original speech, such as voice, emotion, tone, etc. However, such models usually have to be trained on datasets with paired S2ST data, but the public availability of such corpora is extremely limited.

To foster research on such a new generation of S2ST, we introduce a Common Voice-based Speech-to-Speech translation corpus, or CVSS, which includes sentence-level speech-to-speech translation pairs from 21 languages into English. Unlike existing public corpora, CVSS can be directly used for training such direct S2ST models without any extra processing. In “CVSS Corpus and Massively Multilingual Speech-to-Speech Translation”, we describe the dataset design and development, and demonstrate the effectiveness of the corpus through training of baseline direct and cascade S2ST models and showing performance of a direct S2ST model that approaches that of a cascade S2ST model.

Building CVSS
CVSS is directly derived from the CoVoST 2 speech-to-text (ST) translation corpus, which is further derived from the Common Voice speech corpus. Common Voice is a massively multilingual transcribed speech corpus designed for ASR in which the speech is collected by contributors reading text content from Wikipedia and other text corpora. CoVoST 2 further provides professional text translation for the original transcript from 21 languages into English and from English into 15 languages. CVSS builds on these efforts by providing sentence-level parallel speech-to-speech translation pairs from 21 languages into English (shown in the table below).

To facilitate research with different focuses, two versions of translation speech in English are provided in CVSS, both are synthesized using state-of-the-art TTS systems, with each version providing unique value that doesn’t exist in other public S2ST corpora:

CVSS-C: All the translation speech is in a single canonical speaker’s voice. Despite being synthetic, the speech is highly natural, clean, and consistent in speaking style. These properties ease the modeling of the target speech and enable trained models to produce high quality translation speech suitable for general user-facing applications where speech quality is of higher importance than accurately reproducing the speakers' voices.
CVSS-T: The translation speech captures the voice from the corresponding source speech. Each S2ST pair has a similar voice on the two sides, despite being in different languages. Because of this, the dataset is suitable for building models where accurate voice preservation is desired, such as for movie dubbing.

Together with the source speech, the two S2ST datasets contain 1,872 and 1,937 hours of speech, respectively.

Source Language	Code	Source speech (X)	CVSS-C target speech (En)	CVSS-T target speech (En)
French	fr	309.3	200.3	222.3
German	de	226.5	137.0	151.2
Catalan	ca	174.8	112.1	120.9
Spanish	es	157.6	94.3	100.2
Italian	it	73.9	46.5	49.2
Persian	fa	58.8	29.9	34.5
Russian	ru	38.7	26.9	27.4
Chinese	zh	26.5	20.5	22.1
Portuguese	pt	20.0	10.4	11.8
Dutch	nl	11.2	7.3	7.7
Estonian	et	9.0	7.3	7.1
Mongolian	mn	8.4	5.1	5.7
Turkish	tr	7.9	5.4	5.7
Arabic	ar	5.8	2.7	3.1
Latvian	lv	4.9	2.6	3.1
Swedish	sv	4.3	2.3	2.8
Welsh	cy	3.6	1.9	2.0
Tamil	ta	3.1	1.7	2.0
Indonesian	id	3.0	1.6	1.7
Japanese	ja	3.0	1.7	1.8
Slovenian	sl	2.9	1.6	1.9
Total		1,153.2	719.1	784.2

Amount of source and target speech of each X-En pair in CVSS (hours).

In addition to translation speech, CVSS also provides normalized translation text matching the pronunciation in the translation speech (on numbers, currencies, acronyms, etc., see data samples below, e.g., where “100%” is normalized as “one hundred percent” or “King George II” is normalized as “king george the second”), which can benefit both model training as well as standardizing the evaluation.

CVSS is released under the Creative Commons Attribution 4.0 International (CC BY 4.0) license and it can be freely downloaded online.

Data Samples

*Example 1:*
Source audio (French)

Source transcript (French)		Le genre musical de la chanson est entièrement le disco.

CVSS-C translation audio (English)
CVSS-T translation audio (English)

Translation text (English)		The musical genre of the song is 100% Disco.

Normalized translation text (English)		the musical genre of the song is one hundred percent disco


*Example 2:*
Source audio (Chinese)

Source transcript (Chinese)		弗雷德里克王子，英国王室成员，为乔治二世之孙，乔治三世之幼弟。

CVSS-C translation audio (English)
CVSS-T translation audio (English)

Translation text (English)		Prince Frederick, member of British Royal Family, Grandson of King George II, brother of King George III.

Normalized translation text (English)		prince frederick member of british royal family grandson of king george the second brother of king george the third

Baseline Models
On each version of CVSS, we trained a baseline cascade S2ST model as well as two baseline direct S2ST models and compared their performance. These baselines can be used for comparison in future research.

Cascade S2ST: To build strong cascade S2ST baselines, we trained an ST model on CoVoST 2, which outperforms the previous states of the art by +5.8 average BLEU on all 21 language pairs (detailed in the paper) when trained on the corpus without using extra data. This ST model is connected to the same TTS models used for constructing CVSS to compose very strong cascade S2ST baselines (ST → TTS).

Direct S2ST: We built two baseline direct S2ST models using Translatotron and Translatotron 2. When trained from scratch with CVSS, the translation quality from Translatotron 2 (8.7 BLEU) approaches that of the strong cascade S2ST baseline (10.6 BLEU). Moreover, when both use pre-training the gap decreases to only 0.7 BLEU on ASR transcribed translation. These results verify the effectiveness of using CVSS to train direct S2ST models.

Translation quality of baseline direct and cascade S2ST models built on CVSS-C, measured by BLEU on ASR transcription from speech translation. The pre-training was done on CoVoST 2 without other extra data sets.

Conclusion
We have released two versions of multilingual-to-English S2ST datasets, CVSS-C and CVSS-T, each with about 1.9K hours of sentence-level parallel S2ST pairs, covering 21 source languages. The translation speech in CVSS-C is in a single canonical speaker’s voice, while the same in CVSS-T is in voices transferred from the source speech. Each of these datasets provides unique value not existing in other public S2ST corpora.

We built baseline multilingual direct S2ST models and cascade S2ST models on both datasets, which can be used for comparison in future works. To build strong cascade S2ST baselines, we trained an ST model on CoVoST 2, which outperforms the previous states of the art by +5.8 average BLEU when trained on the corpus without extra data. Nevertheless, the performance of the direct S2ST models approaches the strong cascade baselines when trained from scratch, and with only 0.7 BLEU difference on ASR transcribed translation when utilized pre-training. We hope this work helps accelerate the research on direct S2ST.

Acknowledgments
We acknowledge the volunteer contributors and the organizers of the Common Voice and LibriVox projects for their contribution and collection of recordings, the creators of Common Voice, CoVoST, CoVoST 2, Librispeech and LibriTTS corpora for their previous work. The direct contributors to the CVSS corpus and the paper include Ye Jia, Michelle Tadmor Ramanovich, Quan Wang, Heiga Zen. We also thank Ankur Bapna, Yiling Huang, Jason Pelecanos, Colin Cherry, Alexis Conneau, Yonghui Wu, Hadar Shemtov and Françoise Beaufays for helpful discussions and support.

Source: Google AI Blog

Introducing CVSS: A Massively Multilingual Speech-to-Speech Translation Corpus

Posted by Ye Jia and Michelle Tadmor Ramanovich, Software Engineers, Google Research

CVSS-C: All the translation speech is in a single canonical speaker’s voice. Despite being synthetic, the speech is highly natural, clean, and consistent in speaking style. These properties ease the modeling of the target speech and enable trained models to produce high quality translation speech suitable for general user-facing applications where speech quality is of higher importance than accurately reproducing the speakers' voices.
CVSS-T: The translation speech captures the voice from the corresponding source speech. Each S2ST pair has a similar voice on the two sides, despite being in different languages. Because of this, the dataset is suitable for building models where accurate voice preservation is desired, such as for movie dubbing.

Together with the source speech, the two S2ST datasets contain 1,872 and 1,937 hours of speech, respectively.

Source Language	Code	Source speech (X)	CVSS-C target speech (En)	CVSS-T target speech (En)
French	fr	309.3	200.3	222.3
German	de	226.5	137.0	151.2
Catalan	ca	174.8	112.1	120.9
Spanish	es	157.6	94.3	100.2
Italian	it	73.9	46.5	49.2
Persian	fa	58.8	29.9	34.5
Russian	ru	38.7	26.9	27.4
Chinese	zh	26.5	20.5	22.1
Portuguese	pt	20.0	10.4	11.8
Dutch	nl	11.2	7.3	7.7
Estonian	et	9.0	7.3	7.1
Mongolian	mn	8.4	5.1	5.7
Turkish	tr	7.9	5.4	5.7
Arabic	ar	5.8	2.7	3.1
Latvian	lv	4.9	2.6	3.1
Swedish	sv	4.3	2.3	2.8
Welsh	cy	3.6	1.9	2.0
Tamil	ta	3.1	1.7	2.0
Indonesian	id	3.0	1.6	1.7
Japanese	ja	3.0	1.7	1.8
Slovenian	sl	2.9	1.6	1.9
Total		1,153.2	719.1	784.2

Amount of source and target speech of each X-En pair in CVSS (hours).

CVSS is released under the Creative Commons Attribution 4.0 International (CC BY 4.0) license and it can be freely downloaded online.

Data Samples

*Example 1:*
Source audio (French)

Source transcript (French)		Le genre musical de la chanson est entièrement le disco.

CVSS-C translation audio (English)
CVSS-T translation audio (English)

Translation text (English)		The musical genre of the song is 100% Disco.

Normalized translation text (English)		the musical genre of the song is one hundred percent disco


*Example 2:*
Source audio (Chinese)

Source transcript (Chinese)		弗雷德里克王子，英国王室成员，为乔治二世之孙，乔治三世之幼弟。

CVSS-C translation audio (English)
CVSS-T translation audio (English)

Translation text (English)		Prince Frederick, member of British Royal Family, Grandson of King George II, brother of King George III.

Normalized translation text (English)		prince frederick member of british royal family grandson of king george the second brother of king george the third

Source: Google AI Blog

A Dataset for Studying Gender Bias in Translation

Posted by Romina Stella, Product Manager, Google Translate

Advances on neural machine translation (NMT) have enabled more natural and fluid translations, but they still can reflect the societal biases and stereotypes of the data on which they're trained. As such, it is an ongoing goal at Google to develop innovative techniques to reduce gender bias in machine translation, in alignment with our AI Principles.

One research area has been using context from surrounding sentences or passages to improve gender accuracy. This is a challenge because traditional NMT methods translate sentences individually, but gendered information is not always explicitly stated in each individual sentence. For example, in the following passage in Spanish (a language where subjects aren’t always explicitly mentioned), the first sentence refers explicitly to Marie Curie as the subject, but the second one doesn't explicitly mention the subject. In isolation, this second sentence could refer to a person of any gender. When translating to English, however, a pronoun needs to be picked, and the information needed for an accurate translation is in the first sentence.

Spanish Text	Translation to English
Marie Curie nació en Varsovia. Fue la primera persona en recibir dos premios Nobel en distintas especialidades.	Marie Curie was born in Warsaw. She was the first person to receive two Nobel Prizes in different specialties.

Advancing translation techniques beyond single sentences requires new metrics for measuring progress and new datasets with the most common context-related errors. Adding to this challenge is the fact that translation errors related to gender (such as picking the correct pronoun or having gender agreement) are particularly sensitive, because they may directly refer to people and how they self identify.

To help facilitate progress against the common challenges on contextual translation (e.g., pronoun drop, gender agreement and accurate possessives), we are releasing the Translated Wikipedia Biographies dataset, which can be used to evaluate the gender bias of translation models. Our intent with this release is to support long-term improvements on ML systems focused on pronouns and gender in translation by providing a benchmark in which translations’ accuracy can be measured pre- and post-model changes.

A Source of Common Translation Errors
Because they are well-written, geographically diverse, contain multiple sentences, and refer to subjects in the third person (and so contain plenty of pronouns), Wikipedia biographies offer a high potential for common translation errors associated with gender. These often occur when articles refer to a person explicitly in early sentences of a paragraph, but there is no explicit mention of the person in later sentences. Some examples:

*Translation Error*	*Text*	*Translation*
*Pro-drop in Spanish → English*	Marie Curie nació en Varsovia. Recibió el Premio Nobel en 1903 y en 1911.	Marie Curie was born in Warsaw. He received the Nobel Prize in 1903 and in 1911.

*Neutral possessives in Spanish → English*	Marie Curie nació en Varsovia. Su carrera profesional fue desarrollada en Francia.	Marie Curie was born in Warsaw. His professional career was developed in France.

*Gender agreement in English → German*	Marie Curie was born in Warsaw. The distinguished scientist received the Nobel Prize in 1903 and in 1911.	Marie Curie wurde in Varsovia geboren. Der angesehene Wissenschaftler erhielt 1903 und 1911 den Nobelpreis.

*Gender agreement in English → Spanish*	Marie Curie was born in Warsaw. The distinguished scientist received the Nobel Prize in 1903 and in 1911.	Marie Curie nació en Varsovia. El distinguido científico recibió el Premio Nobel en 1903 y en 1911.

Building the Dataset
The Translated Wikipedia Biographies dataset has been designed to analyze common gender errors in machine translation, such as those illustrated above. Each instance of the dataset represents a person (identified in the biographies as feminine or masculine), a rock band or a sports team (considered genderless). Each instance is represented by a long text translation of 8 to 15 connected sentences referring to that central subject (the person, rock band, or sports team). Articles are written in native English and have been professionally translated to Spanish and German. For Spanish, translations were optimized for pronoun-drop, so the same set could be used to analyze pro-drop (Spanish → English) and gender agreement (English → Spanish).

The dataset was built by selecting a group of instances that has equal representation across geographies and genders. To do this, we extracted biographies from Wikipedia according to occupation, profession, job and/or activity. To ensure an unbiased selection of occupations, we chose nine occupations that represented a range of stereotypical gender associations (either feminine, masculine, or neither) based on Wikipedia statistics. Then, to mitigate any geography-based bias, we divided all these instances based on geographical diversity. For each occupation category, we looked to have one candidate per region (using regions from census.gov as a proxy of geographical diversity). When an instance was associated with a region, we checked that the selected person had a relevant relationship with a country that belongs to a designated region (nationality, place of birth, lived for a big portion of their life, etc.). By using this criteria, the dataset contains entries about individuals from more than 90 countries and all regions of the world.

Although gender is non-binary, we focused on having equal representation of “feminine” and “masculine” entities. It's worth mentioning that because the entities are represented as such on Wikipedia, the set doesn't include individuals that identify as non-binary, as, unfortunately, there are not enough instances currently represented in Wikipedia to accurately reflect the non-binary community. To label each instance as "feminine" or "masculine" we relied on the biographical information from Wikipedia, which contained gender-specific references to the person (she, he, woman, son, father, etc.).

After applying all these filters, we randomly selected an instance for each occupation-region-gender triplet. For each occupation, there are two biographies (one masculine and one feminine), for each of the seven geographic regions.

Finally, we added 12 instances with no gender. We picked rock bands and sports teams because they are usually referred to by non-gendered third person pronouns (such as “it” or singular “they”). The purpose of including these instances is to study over triggering, i.e., when models learn that they are rewarded for producing gender-specific pronouns, leading them to produce these pronouns in cases where they shouldn't.

Results and Applications
This dataset enables a new method of evaluation for gender bias reduction in machine translations (introduced in a previous post). Because each instance refers to a subject with a known gender, we can compute the accuracy of the gender-specific translations that refer to this subject. This computation is easier when translating into English (cases of languages with pro-drop or neutral pronouns) since computation is mainly based on gender-specific pronouns in English. In these cases, the gender datasets have resulted in a 67% reduction in errors on context-aware models vs. previous models. As mentioned before, the neutral entities have allowed us to discover cases of over triggering like the usage of feminine or masculine pronouns to refer to genderless entities. This new dataset also enables new research directions into the performance of different models across types of occupations or geographic regions.

As an example, the dataset allowed us to discover the following improvements in an excerpt of the translated biography of Marie Curie from Spanish.

Translation result with the previous NMT model.

Translation result with the new contextual model.

Conclusion
This Translated Wikipedia Biographies dataset is the result of our own studies and work on identifying biases associated with gender and machine translation. This set focuses on a specific problem related to gender bias and doesn't aim to cover the whole problem. It's worth mentioning that by releasing this dataset, we don't aim to be prescriptive in determining what's the optimal approach to address gender bias. This contribution aims to foster progress on this challenge across the global research community.

Acknowledgements
The datasets were built with help from Anja Austermann, Melvin Johnson, Michelle Linch, Mengmeng Niu, Mahima Pushkarna, Apu Shah, Romina Stella, and Kellie Webster.

Source: Google AI Blog

Stabilizing Live Speech Translation in Google Translate

Posted by Naveen Arivazhagan, Senior Software Engineer and Colin Cherry, Staff Research Scientist, Google Research

The transcription feature in the Google Translate app may be used to create a live, translated transcription for events like meetings and speeches, or simply for a story at the dinner table in a language you don’t understand. In such settings, it is useful for the translated text to be displayed promptly to help keep the reader engaged and in the moment.

However, with early versions of this feature the translated text suffered from multiple real-time revisions, which can be distracting. This was because of the non-monotonic relationship between the source and the translated text, in which words at the end of the source sentence can influence words at the beginning of the translation.

Transcribe (old) — Left: Source transcript as it arrives from speech recognition. Right: Translation that is displayed to the user. The frequent corrections made to the translation interfere with the reading experience.

Today, we are excited to describe some of the technology behind a recently released update to the transcribe feature in the Google Translate app that significantly reduces translation revisions and improves the user experience. The research enabling this is presented in two papers. The first formulates an evaluation framework tailored to live translation and develops methods to reduce instability. The second demonstrates that these methods do very well compared to alternatives, while still retaining the simplicity of the original approach. The resulting model is much more stable and provides a noticeably improved reading experience within Google Translate.

Transcribe (new) — Left: Source transcript as it arrives from speech recognition. Right: Translation that is displayed to the user. At the cost of a small delay, the translation now rarely needs to be corrected.

Evaluating Live Translation
Before attempting to make any improvements, it was important to first understand and quantifiably measure the different aspects of the user experience, with the goal of maximizing quality while minimizing latency and instability. In “Re-translation Strategies For Long Form, Simultaneous, Spoken Language Translation”, we developed an evaluation framework for live-translation that has since guided our research and engineering efforts. This work presents a performance measure using the following metrics:

Erasure: Measures the additional reading burden on the user due to instability. It is the number of words that are erased and replaced for every word in the final translation.
Lag: Measures the average time that has passed between when a user utters a word and when the word’s translation displayed on the screen becomes stable. Requiring stability avoids rewarding systems that can only manage to be fast due to frequent corrections.
BLEU score: Measures the quality of the final translation. Quality differences in intermediate translations are captured by a combination of all metrics.

It is important to recognize the inherent trade-offs between these different aspects of quality. Transcribe enables live-translation by stacking machine translation on top of real-time automatic speech recognition. For each update to the recognized transcript, a fresh translation is generated in real time; several updates can occur each second. This approach placed Transcribe at one extreme of the 3 dimensional quality framework: it exhibited minimal lag and the best quality, but also had high erasure. Understanding this allowed us to work towards finding a better balance.

Stabilizing Re-translation
One straightforward solution to reduce erasure is to decrease the frequency with which translations are updated. Along this line, “streaming translation” models (for example, STACL and MILk) intelligently learn to recognize when sufficient source information has been received to extend the translation safely, so the translation never needs to be changed. In doing so, streaming translation models are able to achieve zero erasure.

The downside with such streaming translation models is that they once again take an extreme position: zero erasure necessitates sacrificing BLEU and lag. Rather than eliminating erasure altogether, a small budget for occasional instability may allow better BLEU and lag. More importantly, streaming translation would require retraining and maintenance of specialized models specifically for live-translation. This precludes the use of streaming translation in some cases, because keeping a lean pipeline is an important consideration for a product like Google Translate that supports 100+ languages.

In our second paper, “Re-translation versus Streaming for Simultaneous Translation”, we show that our original “re-translation” approach to live-translation can be fine-tuned to reduce erasure and achieve a more favorable erasure/lag/BLEU trade-off. Without training any specialized models, we applied a pair of inference-time heuristics to the original machine translation models — masking and biasing.

The end of an on-going translation tends to flicker because it is more likely to have dependencies on source words that have yet to arrive. We reduce this by truncating some number of words from the translation until the end of the source sentence has been observed. This masking process thus trades latency for stability, without affecting quality. This is very similar to delay-based strategies used in streaming methods such as Wait-k, but applied only during inference and not during training.

Neural machine translation often “see-saws” between equally good translations, causing unnecessary erasure. We improve stability by biasing the output towards what we have already shown the user. On top of reducing erasure, biasing also tends to reduce lag by stabilizing translations earlier. Biasing interacts nicely with masking, as masking words that are likely to be unstable also prevents the model from biasing toward them. However, this process does need to be tuned carefully, as a high bias, along with insufficient masking, may have a negative impact on quality.

The combination of masking and biasing, produces a re-translation system with high quality and low latency, while virtually eliminating erasure. The table below shows how the metrics react to the heuristics we introduced and how they compare to the other systems discussed above. The graph demonstrates that even with a very small erasure budget, re-translation surpasses zero-flicker streaming translation systems (MILk and Wait-k) trained specifically for live-translation.

*System*	*BLEU*	*Lag (s)*	*Erasure*
Re-translation (old)	20.4	4.1	2.1
+ Stabilization (new)	20.2	4.1	0.1

Evaluation of re-translation on IWSLT test 2018 Engish-German (TED talks) with and without the inference-time stabilization heuristics of masking and biasing. Stabilization drastically reduces erasure. Translation quality, measured in BLEU, is very slightly impacted due to biasing. Despite masking, the effective lag remains the same because the translation stabilizes sooner.

Comparison of re-translation with stabilization and specialized streaming models (Wait-k and MILk) on WMT 14 English-German. The BLEU-lag trade-off curve for re-translation is obtained via different combinations of bias and masking while maintaining an erasure budget of less than 2 words erased for every 10 generated. Re-translation offers better BLEU / lag trade-offs than streaming models which cannot make corrections and require specialized training for each trade-off point.

Conclusion
The solution outlined above returns a decent translation very quickly, while allowing it to be revised as more of the source sentence is spoken. The simple structure of re-translation enables the application of our best speech and translation models with minimal effort. However, reducing erasure is just one part of the story — we are also looking forward to improving the overall speech translation experience through new technology that can reduce lag when the translation is spoken, or that can enable better transcriptions when multiple people are speaking.

Acknowledgements
Thanks to Te I, Dirk Padfield, Pallavi Baljekar, Goerge Foster, Wolfgang Macherey, John Richardson, Kuang-Che Lee, Byran Lin, Jeff Pittman, Sami Iqram, Mengmeng Niu, Macduff Hughes, Chris Kau, Nathan Bain.

Source: Google AI Blog

Recent Advances in Google Translate

Posted by Isaac Caswell and Bowen Liang, Software Engineers, Google Research

Advances in machine learning (ML) have driven improvements to automated translation, including the GNMT neural translation model introduced in Translate in 2016, that have enabled great improvements to the quality of translation for over 100 languages. Nevertheless, state-of-the-art systems lag significantly behind human performance in all but the most specific translation tasks. And while the research community has developed techniques that are successful for high-resource languages like Spanish and German, for which there exist copious amounts of training data, performance on low-resource languages, like Yoruba or Malayalam, still leaves much to be desired. Many techniques have demonstrated significant gains for low-resource languages in controlled research settings (e.g., the WMT Evaluation Campaign), however these results on smaller, publicly available datasets may not easily transition to large, web-crawled datasets.

In this post, we share some recent progress we have made in translation quality for supported languages, especially for those that are low-resource, by synthesizing and expanding a variety of recent advances, and demonstrate how they can be applied at scale to noisy, web-mined data. These techniques span improvements to model architecture and training, improved treatment of noise in datasets, increased multilingual transfer learning through M4 modeling, and use of monolingual data. The quality improvements, which averaged +5 BLEU score over all 100+ languages, are visualized below.

BLEU score of Google Translate models since shortly after its inception in 2006. The improvements since the implementation of the new techniques over the last year are highlighted at the end of the animation.

Advances for Both High- and Low-Resource Languages
Hybrid Model Architecture: Four years ago we introduced the RNN-based GNMT model, which yielded large quality improvements and enabled Translate to cover many more languages. Following our work decoupling different aspects of model performance, we have replaced the original GNMT system, instead training models with a transformer encoder and an RNN decoder, implemented in Lingvo (a TensorFlow framework). Transformer models have been demonstrated to be generally more effective at machine translation than RNN models, but our work suggested that most of these quality gains were from the transformer encoder, and that the transformer decoder was not significantly better than the RNN decoder. Since the RNN decoder is much faster at inference time, we applied a variety of optimizations before coupling it with the transformer encoder. The resulting hybrid models are higher-quality, more stable in training, and exhibit lower latency.

Web Crawl: Neural Machine Translation (NMT) models are trained using examples of translated sentences and documents, which are typically collected from the public web. Compared to phrase-based machine translation, NMT has been found to be more sensitive to data quality. As such, we replaced the previous data collection system with a new data miner that focuses more on precision than recall, which allows the collection of higher quality training data from the public web. Additionally, we switched the web crawler from a dictionary-based model to an embedding based model for 14 large language pairs, which increased the number of sentences collected by an average of 29 percent, without loss of precision.

Modeling Data Noise: Data with significant noise is not only redundant but also lowers the quality of models trained on it. In order to address data noise, we used our results on denoising NMT training to assign a score to every training example using preliminary models trained on noisy data and fine-tuned on clean data. We then treat training as a curriculum learning problem — the models start out training on all data, and then gradually train on smaller and cleaner subsets.

Advances That Benefited Low-Resource Languages in Particular
Back-Translation: Widely adopted in state-of-the-art machine translation systems, back-translation is especially helpful for low-resource languages, where parallel data is scarce. This technique augments parallel training data (where each sentence in one language is paired with its translation) with synthetic parallel data, where the sentences in one language are written by a human, but their translations have been generated by a neural translation model. By incorporating back-translation into Google Translate, we can make use of the more abundant monolingual text data for low-resource languages on the web for training our models. This is especially helpful in increasing fluency of model output, which is an area in which low-resource translation models underperform.

M4 Modeling: A technique that has been especially helpful for low-resource languages has been M4, which uses a single, giant model to translate between all languages and English. This allows for transfer learning at a massive scale. As an example, a lower-resource language like Yiddish has the benefit of co-training with a wide array of other related Germanic languages (e.g., German, Dutch, Danish, etc.), as well as almost a hundred other languages that may not share a known linguistic connection, but may provide useful signal to the model.

Judging Translation Quality
A popular metric for automatic quality evaluation of machine translation systems is the BLEU score, which is based on the similarity between a system’s translation and reference translations that were generated by people. With these latest updates, we see an average BLEU gain of +5 points over the previous GNMT models, with the 50 lowest-resource languages seeing an average gain of +7 BLEU. This improvement is comparable to the gain observed four years ago when transitioning from phrase-based translation to NMT.

Although BLEU score is a well-known approximate measure, it is known to have various pitfalls for systems that are already high-quality. For instance, several works have demonstrated how the BLEU score can be biased by translationese effects on the source side or target side, a phenomenon where translated text can sound awkward, containing attributes (like word order) from the source language. For this reason, we performed human side-by-side evaluations on all new models, which confirmed the gains in BLEU.

In addition to general quality improvements, the new models show increased robustness to machine translation hallucination, a phenomenon in which models produce strange “translations” when given nonsense input. This is a common problem for models that have been trained on small amounts of data, and affects many low-resource languages. For example, when given the string of Telugu characters “ష ష ష ష ష ష ష ష ష ష ష ష ష ష ష”, the old model produced the nonsensical output “Shenzhen Shenzhen Shaw International Airport (SSH)”, seemingly trying to make sense of the sounds, whereas the new model correctly learns to transliterate this as “Sh sh sh sh sh sh sh sh sh sh sh sh sh sh sh sh sh”.

Conclusion
Although these are impressive strides forward for a machine, one must remember that, especially for low-resource languages, automatic translation quality is far from perfect. These models still fall prey to typical machine translation errors, including poor performance on particular genres of subject matter (“domains”), conflating different dialects of a language, producing overly literal translations, and poor performance on informal and spoken language.

Nonetheless, with this update, we are proud to provide automatic translations that are relatively coherent, even for the lowest-resource of the 108 supported languages. We are grateful for the research that has enabled this from the active community of machine translation researchers in academia and industry.

Acknowledgements
This effort is built on contributions from Tao Yu, Ali Dabirmoghaddam, Klaus Macherey, Pidong Wang, Ye Tian, Jeff Klingner, Jumpei Takeuchi, Yuichiro Sawai, Hideto Kazawa, Apu Shah, Manisha Jain, Keith Stevens, Fangxiaoyu Feng, Chao Tian, John Richardson, Rajat Tibrewal, Orhan Firat, Mia Chen, Ankur Bapna, Naveen Arivazhagan, Dmitry Lepikhin, Wei Wang, Wolfgang Macherey, Katrin Tomanek, Qin Gao, Mengmeng Niu, and Macduff Hughes.

Source: Google AI Blog

Exploring Massively Multilingual, Massive Neural Machine Translation

Posted by Ankur Bapna, Software Engineer and Orhan Firat, Research Scientist, Google Research

“... perhaps the way [of translation] is to descend, from each language, down to the common base of human communication — the real but as yet undiscovered universal language — and then re-emerge by whatever particular route is convenient.” — Warren Weaver, 1949

Over the last few years there has been enormous progress in the quality of machine translation (MT) systems, breaking language barriers around the world thanks to the developments in neural machine translation (NMT). The success of NMT however, owes largely to the great amounts of supervised training data. But what about languages where data is scarce, or even absent? Multilingual NMT, with the inductive bias that “the learning signal from one language should benefit the quality of translation to other languages”, is a potential remedy.

Multilingual machine translation processes multiple languages using a single translation model. The success of multilingual training for data-scarce languages has been demonstrated for automatic speech recognition and text-to-speech systems, and by prior research on multilingual translation [1,2,3]. We previously studied the effect of scaling up the number of languages that can be learned in a single neural network, while controlling the amount of training data per language. But what happens once all constraints are removed? Can we train a single model using all of the available data, despite the huge differences across languages in data size, scripts, complexity and domains?

In “Massively Multilingual Neural Machine Translation in the Wild: Findings and Challenges” and follow-up papers [4,5,6,7], we push the limits of research on multilingual NMT by training a single NMT model on 25+ billion sentence pairs, from 100+ languages to and from English, with 50+ billion parameters. The result is an approach for massively multilingual, massive neural machine translation (M4) that demonstrates large quality improvements on both low- and high-resource languages and can be easily adapted to individual domains/languages, while showing great efficacy on cross-lingual downstream transfer tasks.

Massively Multilingual Machine Translation
Though data skew across language-pairs is a great challenge in NMT, it also creates an ideal scenario in which to study transfer, where insights gained through training on one language can be applied to the translation of other languages. On one end of the distribution, there are high-resource languages like French, German and Spanish where there are billions of parallel examples, while on the other end, supervised data for low-resource languages such as Yoruba, Sindhi and Hawaiian, is limited to a few tens of thousands.

The data distribution over all language pairs (in log scale) and the relative translation quality (BLEU score) of the bilingual baselines trained on each one of these specific language pairs.

Once trained using all of the available data (25+ billion examples from 103 languages), we observe strong positive transfer towards low-resource languages, dramatically improving the translation quality of 30+ languages at the tail of the distribution by an average of 5 BLEU points. This effect is already known, but surprisingly encouraging, considering the comparison is between bilingual baselines (i.e., models trained only on specific language pairs) and a single multilingual model with representational capacity similar to a single bilingual model. This finding hints that massively multilingual models are effective at generalization, and capable of capturing the representational similarity across a large body of languages.

Translation quality comparison of a single massively multilingual model against bilingual baselines that are trained for each one of the 103 language pairs.

In our EMNLP’19 paper [5], we compare the representations of multilingual models across different languages. We find that multilingual models learn shared representations for linguistically similar languages without the need for external constraints, validating long-standing intuitions and empirical results that exploit these similarities. In [6], we further demonstrate the effectiveness of these learned representations on cross-lingual transfer on downstream tasks.

Visualization of the clustering of the encoded representations of all 103 languages, based on representational similarity. Languages are color-coded by their linguistic family.

Building Massive Neural Networks
As we increase the number of low-resource languages in the model, the quality of high-resource language translations starts to decline. This regression is recognized in multi-task setups, arising from inter-task competition and the unidirectional nature of transfer (i.e., from high- to low-resource). While working on better learning and capacity control algorithms to mitigate this negative transfer, we also extend the representational capacity of our neural networks by making them bigger by increasing the number of model parameters to improve the quality of translation for high-resource languages.

Numerous design choices can be made to scale neural network capacity, including adding more layers or making the hidden representations wider. Continuing our study on training deeper networks for translation, we utilized GPipe [4] to train 128-layer Transformers with over 6 billion parameters. Increasing the model capacity resulted in significantly improved performance across all languages by an average of 5 BLEU points. We also studied other properties of very deep networks, including the depth-width trade-off, trainability challenges and design choices for scaling Transformers to over 1500 layers with 84 billion parameters.

While scaling depth is one approach to increasing model capacity, exploring architectures that can exploit the multi-task nature of the problem is a very plausible complementary way forward. By modifying the Transformer architecture through the substitution of the vanilla feed-forward layers with sparsely-gated mixture of experts, we drastically scale up the model capacity, allowing us to successfully train and pass 50 billion parameters, which further improved translation quality across the board.

Translation quality improvement of a single massively multilingual model as we increase the capacity (number of parameters) compared to 103 individual bilingual baselines.

Making M4 Practical
It is inefficient to train large models with extremely high computational costs for every individual language, domain or transfer task. Instead, we present methods [7] to make these models more practical by using capacity tunable layers to adapt a new model to specific languages or domains, without altering the original.

Next Steps
At least half of the 7,000 languages currently spoken will no longer exist by the end of this century^*. Can multilingual machine translation come to the rescue? We see the M4 approach as a stepping stone towards serving the next 1,000 languages; starting from such multilingual models will allow us to easily extend to new languages, domains and down-stream tasks, even when parallel data is unavailable. Indeed the path is rocky, and on the road to universal MT many promising solutions appear to be interdisciplinary. This makes multilingual NMT a plausible test bed for machine learning practitioners and theoreticians interested in exploring the annals of multi-task learning, meta-learning, training dynamics of deep nets and much more. We still have a long way to go.

Acknowledgements
This effort is built on contributions from Naveen Arivazhagan, Dmitry Lepikhin, Melvin Johnson, Maxim Krikun, Mia Chen, Yuan Cao, Yanping Huang, Sneha Kudugunta, Isaac Caswell, Aditya Siddhant, Wei Wang, Roee Aharoni, Sébastien Jean, George Foster, Colin Cherry, Wolfgang Macherey, Zhifeng Chen and Yonghui Wu. We would also like to acknowledge support from the Google Translate, Brain, and Lingvo development teams, Jakob Uszkoreit, Noam Shazeer, Hyouk Joong Lee, Dehao Chen, Youlong Cheng, David Grangier, Colin Raffel, Katherine Lee, Thang Luong, Geoffrey Hinton, Manisha Jain, Pendar Yousefi and Macduff Hughes.

* The Cambridge Handbook of Endangered Languages (Austin and Sallabank, 2011). ↩

Source: Google AI Blog

Robust Neural Machine Translation

Posted by Yong Cheng, Software Engineer, Google Research

In recent years, neural machine translation (NMT) using Transformer models has experienced tremendous success. Based on deep neural networks, NMT models are usually trained end-to-end on very large parallel corpora (input/output text pairs) in an entirely data-driven fashion and without the need to impose explicit rules of language.

Despite this huge success, NMT models can be sensitive to minor perturbations of the input, which can manifest as a variety of different errors, such as under-translation, over-translation or mistranslation. For example, given a German sentence, the state-of-the-art NMT model, Transformer, will yield a correct translation.

“Der Sprecher des Untersuchungsausschusses hat angekündigt, vor Gericht zu ziehen, falls sich die geladenen Zeugen weiterhin weigern sollten, eine Aussage zu machen.”

(Machine translation to English: “The spokesman of the Committee of Inquiry has announced that if the witnesses summoned continue to refuse to testify, he will be brought to court.”),

But, when we apply a subtle change to the input sentence, say from geladenen to the synonym vorgeladenen, the translation becomes very different (and in this case, incorrect):

“Der Sprecher des Untersuchungsausschusses hat angekündigt, vor Gericht zu ziehen, falls sich die vorgeladenen Zeugen weiterhin weigern sollten, eine Aussage zu machen.”

(Machine translation to English: “The investigative committee has announced that he will be brought to justice if the witnesses who have been invited continue to refuse to testify.”).

This lack of robustness in NMT models prevents many commercial systems from being applicable to tasks that cannot tolerate this level of instability. Therefore, learning robust translation models is not just desirable, but is often required in many scenarios. Yet, while the robustness of neural networks has been extensively studied in the computer vision community, only a few prior studies on learning robust NMT models can be found in literature.

In “Robust Neural Machine Translation with Doubly Adversarial Inputs” (to appear at ACL 2019), we propose an approach that uses generated adversarial examples to improve the stability of machine translation models against small perturbations in the input. We learn a robust NMT model to directly overcome adversarial examples generated with knowledge of the model and with the intent of distorting the model predictions. We show that this approach improves the performance of the NMT model on standard benchmarks.

Training a Model with AdvGen
An ideal NMT model would generate similar translations for separate inputs that exhibit small differences. The idea behind our approach is to perturb a translation model with adversarial inputs in the hope of improving the model’s robustness. It does this using an algorithm called Adversarial Generation (AdvGen), which generates plausible adversarial examples for perturbing the model and then feeds them back into the model for defensive training. While this method is inspired by the idea of generative adversarial networks (GANs), it does not rely on a discriminator network, but simply applies the adversarial example in training, effectively diversifying and extending the training set.

The first step is to perturb the model using AdvGen. We start by using Transformer to calculate the translation loss based on a source input sentence, a target input sentence and a target output sentence. Then AdvGen randomly selects some words in the source sentence, assuming a uniform distribution. Each word has an associated list of similar words, i.e., candidates that can be used for substitution, from which AdvGen selects the word that is most likely to introduce errors in Transformer output. Then, this generated adversarial sentence is fed back into Transformer, initiating the defense stage.

First, the Transformer model is applied to an input sentence (lower left) and, in conjunction with the target output sentence (above right) and target input sentence (middle right; beginning with the placeholder “<sos>”), the translation loss is calculated. The AdvGen function then takes the source sentence, word selection distribution, word candidates, and the translation loss as inputs to construct an adversarial source example.

During the defend stage, the adversarial sentence is fed back into the Transformer model. Again the translation loss is calculated, but this time using the adversarial source input. Using the same method as above, AdvGen uses the target input sentence, word replacement candidates, the word selection distribution calculated by the attention matrix, and the translation loss to construct an adversarial target example.

In the defense stage, the adversarial source example serves as input to the Transformer model, and the translation loss is calculated. AdvGen then uses the same method as above to generate an adversarial target example from the target input.

Finally, the adversarial sentence is fed back into Transformer and the robustness loss using the adversarial source example, the adversarial target input example and the target sentence is calculated. If the perturbation led to a significant loss, the loss is minimized so that when the model is confronted with similar perturbations, it will not repeat the same mistake. On the other hand, if the perturbation leads to a low loss, nothing happens, indicating that the model can already handle this perturbation.

Model Performance
We demonstrate the effectiveness of our approach by applying it to the standard Chinese-English and English-German translation benchmarks. We observed a notable improvement of 2.8 and 1.6 BLEU points, respectively, compared to the competitive Transformer model, achieving a new state-of-the-art performance.

Comparison of Transformer model (Vaswani et al., 2017) on standard benchmarks.

We then evaluate our model on a noisy dataset, generated using a procedure similar to that described for AdvGen. We take an input clean dataset, such as that used on standard translation benchmarks, and randomly select words for similar word substitution. We find that our model exhibits improved robustness compared to other recent models.

Comparison of Transformer, Miyao et al. and Cheng et al. on artificial noisy inputs.

These results show that our method is able to overcome small perturbations in the input sentence and improve the generalization performance. It outperforms competitive translation models and achieves state-of-the-art translation performance on standard benchmarks. We hope our translation model will serve as a robust building block for improving many downstream tasks, especially when those are sensitive or intolerant to imperfect translation input.

Acknowledgements
This research was conducted by Yong Cheng, Lu Jiang and Wolfgang Macherey. Additional thanks go to our leadership Andrew Moore and Julia (Wenli) Zhu‎.