A Smorgasbord of Features to Combine Phrase-Based and Neural Machine Translation

Superiority of neural machine translation (NMT) and phrase-based statistical machine translation (PBSMT) depends on the translation task. For some translation tasks, such as those involving low-resource language pairs or close languages, NMT may underperform PBSMT. In order to have a translation system that performs consistently better regardless of the translation task, recent work proposed to combine PBSMT and NMT approaches. In this paper, we propose an empirical comparison of the most popular existing approaches that combine PBSMT and NMT. Despite its simplicity, our simple reranking system using a smorgasbord of informative features significantly and consistently outperforms other methods, even for translation tasks where PBSMT and NMT produce translations of a very different quality.