I would say it's because the more common letters are shifted to where it's easier to get to them, but that can't be right because the QWERTY keyboard disregards letter occurrence entirely.
"i know the french keyboard, why the *beep* do people have to switch keys for each lang?
that's stupid... "
you are stupid and probably dont know much about languages or think about them. there is a system behind them. you need certain letters in a language and they are placed so that you can type words easily. the keyboard could also be A B C D E F G A ... but that just doesnt work and its complicated.
if french people use some english keyboard its pretty complicated for them and not really easy and FAST to type words. so please just THINK ABOUT IT FIRST before you say something is stupid
I would have said that as well, but why are they changed for non-English languages when there's no regard for letter frequency on the US/UK one? Off the top of my head, the most common letters are ETAOIN-SHRDLU-CMFGYP (and I can't remember the rest), and very few of the ones near the top of the list are on the home row.