Automatic machine translation (MT) metrics are widely used to distinguish the translation qualities of machine translation systems across relatively large test sets (system-level evaluation). However, it is unclear if automatic metrics are reliable at distinguishing good translations from bad translations at the sentence level (segment-level evaluation). In this paper, we investigate how useful MT metrics are at detecting the success of a machine translation component when placed in a larger platform with a downstream task. We evaluate the segment-level performance of the most widely used MT metrics (chrF, COMET, BERTScore, etc.) on three downstream cross-lingual tasks (dialogue state tracking, question answering, and semantic parsing). For each task, we only have access to a monolingual task-specific model. We calculate the correlation between the metric's ability to predict a good/bad translation with the success/failure on the final task for the Translate-Test setup. Our experiments demonstrate that all metrics exhibit negligible correlation with the extrinsic evaluation of the downstream outcomes. We also find that the scores provided by neural metrics are not interpretable mostly because of undefined ranges. Our analysis suggests that future MT metrics be designed to produce error labels rather than scores to facilitate extrinsic evaluation.

本文研究了自动机器翻译度量在句子级别（段落级别评估）中区分好的翻译和坏的翻译的可靠性，并研究了在较大平台中放置机器翻译组件的成功率检测中MT度量的有用性。我们在三个下游跨语言任务（对话状态跟踪，问题回答和语义分析）上评估了最广泛使用的MT度量（chrF，COMET，BERTScore等）的段落级别性能。我们的实验表明，所有的度量标准与下游结果的内在评估显示出微不足道的相关性。我们还发现，神经度量提供的分数大多数不是可解释的，因为其值域未定义。我们的分析表明，将来的MT指标应该被设计成产生错误标签而不是得分，以便于外在评估。

机器翻译指标外部评估