DOCmT5: Document-Level Pretraining of Multilingual Language Models.

In this paper, we introduce DOCmT5, a multilingual sequence-to-sequence language model pre-trained with large scale parallel documents. While previous approaches have focused on leveraging sentence-level parallel data, we try to build a general-purpose pre-trained model that can understand and generate long documents. We propose a simple and effective pre-training objective - Document Reordering Machine Translation (DrMT), in which the input documents that are shuffled and masked need to be translated. DrMT brings consistent improvements over strong baselines on a variety of document-level generation tasks, including over 12 BLEU points for seen-language-pair document-level MT, over 7 BLEU points for unseen-language-pair document-level MT and over 3 ROUGE-1 points for seen-language-pair cross-lingual summarization. We achieve state-of-the-art (SOTA) on WMT20 De-En and IWSLT15 Zh-En document translation tasks. We also conduct extensive analysis on various factors for document pre-training, including (1) the effects of pre-training data quality and (2) The effects of combining mono-lingual and cross-lingual pre-training. We plan to make our model checkpoints publicly available.