The target sentence supplied by Google Translate is not and must never be mistaken for the “correct translation.” That’s not just because no such thing as a “correct translation” really exists. It’s also because Google Translate gives only an expression consisting of the most probable equivalent phrases as computed by its analysis of an astronomically large set of paired sentences trawled from the Web.
The data comes in large part from the documentation of international organizations. Thousands of human translators working for the United Nations and the European Union and so forth have spent millions of hours producing precisely those pairings that Google Translate is now able to cherry-pick. The human translations have to come first for Google Translate to have anything to work with.
Op-Ed Contributor - Google Translate vs. the Humans - NYTimes.com