Language Agnostic Multilingual Information Retrieval with Contrastive Learning

Multilingual information retrieval is challenging due to the lack of training datasets for many low-resource languages. We present an effective method by leveraging parallel and non-parallel corpora to improve the pretrained multilingual language models' cross-lingual transfer ability for information retrieval. We design the semantic contrastive loss as regular contrastive learning to improve the cross-lingual alignment of parallel sentence pairs, and we propose a new contrastive loss, the language contrastive loss, to leverage both parallel corpora and non-parallel corpora to further improve multilingual representation learning. We train our model on an English information retrieval dataset, and test its zero-shot transfer ability to other languages. Our experiment results show that our method brings significant improvement to prior work on retrieval performance, while it requires much less computational effort. Our model can work well even with a small number of parallel corpora. And it can be used as an add-on module to any backbone and other tasks. Our code is available at: https://github.com/xiyanghu/multilingualIR.