We present CORA, a Cross-lingual Open-Retrieval Answer Generation model that can answer questions across many languages even when language-specific annotated data or knowledge sources are unavailable. We introduce a new dense passage retrieval algorithm that is trained to retrieve documents across languages for a question. Combined with a multilingual autoregressive generation model, CORA answers directly in the target language without any translation or in-language retrieval modules as used in prior work. We propose an iterative training method that automatically extends annotated data available only in high-resource languages to low-resource ones. Our results show that CORA substantially outperforms the previous state of the art on multilingual open question answering benchmarks across 26 languages, 9 of which are unseen during training. Our analyses show the significance of cross-lingual retrieval and generation in many languages, particularly under low-resource settings.

本研究提出 Cross-lingual Open-Retrieval Answer Generation (CORA) 模型，它是第一个可以回答跨多种语言问题的问答模型，利用密集型检索算法，与多语言自回归生成模型相结合，即可实现直接在目标语言下回答问题，获得了显著的效果提升，特别是在低资源环境下。

跨语言密集文段检索的多语言问答模型