BLEU checks how many words/phrases in the candidate appear in the reference, ensuring that words aren't overcounted.
Avoid using BLEU as the only final arbiter of translation quality for production decisions or to evaluate adequacy in isolation. bleu+pdf+work
To the casual observer, it was just a document. To Elias, a senior computational linguist, it was a corpse. BLEU checks how many words/phrases in the candidate