Leveraging Monolingual Data with Self-Supervision for Multilingual Neural Machine Translation
Paper · 2020 · Aditya Siddhant, Ankur Bapna, Yuan Cao et al.
Summary
Multilingual NMT helps low-resource languages by transferring knowledge from high-resource ones, but it usually ignores monolingual text. Self-supervised pre-training, in contrast, uses monolingual text but not multilingual parallel data. Siddhant et al. combine the two. They train a single Transformer on parallel data with a translation objective and, at the same time, on monolingual data with an adapted MASS denoising objective. The data covers 15 WMT languages translated to and from English.
Adding monolingual data improves every language pair, with the largest gains for very low-resource languages such as Kazakh, Turkish and Gujarati. It also improves zero-shot translation between non-English pairs, bringing it close to pivot-based systems without any alignment or adversarial losses. When a language's parallel data is removed entirely, monolingual data alone still produces strong translation quality for that language. This makes it practical to add new languages to existing multilingual models without parallel corpora or back-translation.
Key points
- Data: WMT parallel data for 30 English-centric pairs, ranging from over 60M sentence pairs (En-Cs) to about 10k (En-Gu). Extra monolingual text for 16 languages comes from news-crawl, common-crawl, europarl-v9, wikidump and other sources, ranging from 2M sentences (Zh) to 270M (De).
- Setup:
- Transformer Big (375M parameters) in Tensorflow-Lingvo.
- Shared 64k SentencePiece vocabulary.
- Target-language
<2xx>token. - Temperature sampling with T = 5 for parallel data.
- Equal 50/50 mix of parallel batches and MASS (monolingual) batches.
- Low-resource gains: For the lowest-resource languages, monolingual data adds roughly 3–5 BLEU for en→xx and more than 5 BLEU for xx→en over the supervised multilingual model.
- Zero-shot: Zero-shot quality rises by about 3–6 BLEU. For example, fr→de in the 30-language model improves from 11.8 to 18.5 BLEU, against 21.9 for pivoting.
- New languages: Using only monolingual data for Romanian gives 33.0 BLEU on WMT ro→en, versus 33.2 with full supervision. This beats XLM by more than 1.5 BLEU and matches bilingual MASS, with no back-translation.
Institutions
📚 Shelves 4The field of science this work belongs to (OpenAlex fields).Computer Science · 9,086 worksArtificial Intelligence · 8,889 worksArts and Humanities · 9,296 worksLanguage and Linguistics · 9,206 works
🧭 Topics 2Research subjects and languages the work is about.Machine translation · 958 worksMultilingual & cross-lingual NLP · 467 works
Cite
Cite as Aditya Siddhant, Ankur Bapna, Yuan Cao, Orhan Firat, Mia Chen, Sneha Kudugunta, Naveen Arivazhagan and Yonghui Wu. 2020. Leveraging Monolingual Data with Self-Supervision for Multilingual Neural Machine Translation. Proceedings of the 58th Annual Meeting of the Association for Computational Linguistics.
@inproceedings{siddhant2020leveraging,
title = {{Leveraging Monolingual Data with Self-Supervision for Multilingual Neural Machine Translation}},
author = {Aditya Siddhant, Ankur Bapna, Yuan Cao, Orhan Firat, Mia Chen, Sneha Kudugunta, Naveen Arivazhagan and Yonghui Wu},
booktitle = {Proceedings of the 58th Annual Meeting of the Association for Computational Linguistics},
year = {2020},
doi = {10.18653/v1/2020.acl-main.252},
url = {https://doi.org/10.18653/v1/2020.acl-main.252}
}References
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