Well, I did not actualy made the "vocal twice as loud as before". This is just something that could be done, in theory, IF the mixes are exactly the same.

I still did not find a way to remove languages, or even to get the music free of vocals, even if we have two exact same mixes (minus different languages). But of course it would make it easier to do experiences and maybe find a way.

EDIT: by the way if someone knows a DVD of a movie where two mixes are exactly 100% the same frequencies, only with different languages I'd be interested to know about it.