mmT5: Modular Multilingual Pre-Training Solves Source Language Hallucinations
Jonas H. Pfeiffer, Francesco Piccinno, Massimo Nicosia, Xinyi Wang, Machel Reid, Sebastian Ruder · 2023
Multilingual sequence-to-sequence models perform poorly with increased language coverage and fail to consistently generate text in the correct target language in few-shot settings.To address these challenges, we propose mmT5, a modular multilingual sequence-to-sequence model.mmT5 utilizes language-specific modules during pre-training, which disentangle language-specific information from language-agnostic information.We identify representation drift during fine-tuning as a key limitation of modular generative models and develop strategies that enable effective zero-shot transfer.Our model outperforms mT5 at the same parameter sizes by a large margin on representative natural language understanding and generation tasks in 40+ languages.Compared to mT5, mmT5 raises the rate of generating text in the correct language under zero-shot settings from 7% to 99%, thereby greatly alleviating the source language hallucination problem.