High Quality Content by WIKIPEDIA articles! BLEU (Bilingual Evaluation Understudy) is an algorithm for evaluating the quality of text which has been machine-translated from one natural language to another. Quality is considered to be the correspondence between a machine`s output and that of a human: "the closer a machine translation is to a professional human translation, the better it is". BLEU was one of the first metrics to achieve a high correlation with human judgements of quality, and remains one of the most popular.