Scores are not absolute, for two reasons.

It should be noted that GT alters its vocabulary choice on the fly, so the words chosen to translate a phrase may not be those selected in a longer sentence for example, “run of the mill” is represented in French by “course du moulin” in isolation, and “course de l’usine” when translating a longer tweet (both completely wrong), and other instances might produce other results. Nor did we test full sentences, which add a lot of complexity to scoring, since translations might include both correct and incorrect elements moreover, humans can translate the same sentence many ways, making it impossible to impose a gold standard for full sentences, especially across dozens of languages. Although GT does not advertise itself as a dictionary, single-word lookups are a major proportion of real world uses of the service. We did not test single words, which can be highly ambiguous (for example, right = correct, legal entitlement, politically conservative, not left, etc.), and therefore too arbitrary in isolation. We tested clusters of two or more words that often occur together, and that have a meaning that is generally discernable when they do (as can be readily seen in Twitter searches) for example, tweets with “out cold” almost always imply unconsciousness.

Google translation in french