I really think it depends on the language. Some are significantly more way of the mark than others.
My thoughts on this would be that it can be disabled at any time in the message system. So the menu etc can be still in the end users language but the message system can be in either their language or the games main language.
I have players from across europe, north & south america. The feedback from them is that they would probably use their language for the game so menu etc but keep interaction with other players in english