Pre-trained multilingual contextual embeddings have demonstrated state-of-the-art performance in zero-shot cross-lingual transfer learning, where multilingual BERT is fine-tuned on some source language (typically English) and evaluated on a different target language. However, published results for baseline mBERT zero-shot accuracy vary as much as 17 points on the MLDoc classification task across four papers. We show that the standard practice of using English dev accuracy for model selection in the zero-shot setting makes it difficult to obtain reproducible results on the MLDoc and XNLI tasks. English dev accuracy is often uncorrelated (or even anti-correlated) with target language accuracy, and zero-shot cross-lingual performance varies greatly within the same fine-tuning run and between different fine-tuning runs. We recommend providing oracle scores alongside the zero-shot results: still fine-tune using English, but choose a checkpoint with the target dev set. Reporting this upper bound makes results more consistent by avoiding the variation from bad checkpoints.

本文研究了多语言语境嵌入在零样本跨语言迁移学习上的表现，并发现使用英语进行零样本设置时很难获得可重复的结果和一致的检查点，建议在零样本结果旁边提供oracle分数，通过避免任意差的检查点使结果更一致。

关于上下文嵌入零样本跨语言评估的不使用英语开发