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Phrase-Based & Neural Unsupervised Machine Translation

2018-04-20EMNLP 2018Code Available0· sign in to hype

Guillaume Lample, Myle Ott, Alexis Conneau, Ludovic Denoyer, Marc'Aurelio Ranzato

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Abstract

Machine translation systems achieve near human-level performance on some languages, yet their effectiveness strongly relies on the availability of large amounts of parallel sentences, which hinders their applicability to the majority of language pairs. This work investigates how to learn to translate when having access to only large monolingual corpora in each language. We propose two model variants, a neural and a phrase-based model. Both versions leverage a careful initialization of the parameters, the denoising effect of language models and automatic generation of parallel data by iterative back-translation. These models are significantly better than methods from the literature, while being simpler and having fewer hyper-parameters. On the widely used WMT'14 English-French and WMT'16 German-English benchmarks, our models respectively obtain 28.1 and 25.2 BLEU points without using a single parallel sentence, outperforming the state of the art by more than 11 BLEU points. On low-resource languages like English-Urdu and English-Romanian, our methods achieve even better results than semi-supervised and supervised approaches leveraging the paucity of available bitexts. Our code for NMT and PBSMT is publicly available.

Tasks

Benchmark Results

DatasetModelMetricClaimedVerifiedStatus
WMT2014 English-FrenchUnsupervised PBSMTBLEU score28.11Unverified
WMT2014 English-FrenchUnsupervised NMT + TransformerBLEU score25.14Unverified
WMT2014 English-FrenchPBSMT + NMTBLEU score27.6Unverified
WMT2014 English-GermanPBSMT + NMTBLEU score20.23Unverified
WMT2014 English-GermanUnsupervised PBSMTBLEU score17.94Unverified
WMT2014 English-GermanUnsupervised NMT + TransformerBLEU score17.16Unverified
WMT2016 English-RomanianPBSMT + NMTBLEU score25.13Unverified
WMT2016 English-RomanianUnsupervised PBSMTBLEU score21.33Unverified
WMT2016 English-RomanianUnsupervised NMT + TransformerBLEU score21.18Unverified
WMT2016 English-RussianPBSMT + NMTBLEU score13.76Unverified
WMT2016 English-RussianUnsupervised NMT + TransformerBLEU score7.98Unverified
WMT2016 English-RussianUnsupervised PBSMTBLEU score13.37Unverified

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