There should be a tutorial popup when going through the Duty Finder the first time to indicate that you can actually change the language settings, but it should be made extremely clear that if you cannot communicate in that language that it is rude to do so.

It should not put them all by default because then you will end up in groups with people you cannot communicate with.

Using the language setting as a way to "speed up" your queue times (if you cannot communicate in that language) is rude at best.