Language-related issues for NMT and PBMT for English-German and English-Serbian

This work presents an extensive comparison of language-related problems for neural machine translation (NMT) and phrase-based machine translation (PBMT) for German-to-English, English-to-German and English-to-Serbian. The explored issues are related both to the characteristics of the languages as well as to the (machine) translation process and, although related, go beyond typical translation error classes. It is shown that the main advantage of the NMT approach consists of better generating verb forms, avoiding verb omissions, as well as better handling of English noun collocations and negation. It is also shown that the main obstacles for the NMT system are prepositions, translation of English (source) ambiguous words and generating English (target) continuous and perfect tenses. In addition, preliminary experiments show that a number of issues are complementary, i.e., not occurring in the same segments and/or in the same form. This means that a combination or hybridisation of the NMT and PBMT approaches is a promising direction for improving both types of systems.