A detailed error analysis is a fundamental step in every natural language processing task, as to be able to diagnose what went wrong will provide cues to decide which research directions are to be followed. In this paper we focus on error analysis in Machine Translation (MT). We significantly extend previous error taxonomies so that translation errors associated with Romance language specificities can be accommodated. Furthermore, based on the proposed taxonomy, we carry out an extensive analysis of the errors generated by four different systems: two mainstream online translation systems Google Translate (Statistical) and Systran (Hybrid Machine Translation), and two in-house MT systems, in three scenarios representing different challenges in the translation from English to European Portuguese. Additionally, we comment on how distinct error types differently impact translation quality.
