I’m in France, and when I launched the game for the first time it was in french. Seems normal. But I don’t like the french voices, and having the abilities and weapons original name is better for the forums, so I asked steam to change the language to english.
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Yes, you know what happens just now … it downloads THE ENTIRE GAME again, just for changing the language ! 
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EDIT: i’m sorry, steam showed it was downloading the entire game, but finaly downloaded 296 Mo.