An Explainable Evaluation of Unsupervised Transfer Learning for Parallel Sentences Mining

The parallel sentences are known as very important resources for training cross-lingual natural language process applications, such as machine translation (MT) systems. However, these resources are not available for many low-resource language pairs. Existing methods mined parallel sentences using transfer learning. Although several attempts can get a good performance, they are not able to explain why transfer learning can help mining parallel sentences for low-resource language pairs. In this paper, we propose an explainable evaluation to quantity why transfer learning is useful for parallel sentence mining. Besides, we propose a novel unsupervised transfer learning that can maintain the robustness of transfer learning. Experiments show that our proposed method improves the performance of mined parallel sentences compared with previous methods in a standard evaluation set. In particular, we achieve good results at two real-world low-resource language pairs.