An American studio would have no problem at all casting a movie in France, a great deal of French actors would love (or do love) to play in blockbusters from time to time (especially since there are much fewer big budget/entertainment movies shot in Europe). The studios won't do it because their home market would never go see such a movie not filmed in English (not for a blockbuster, certainly).

Gérard Depardieu - the biggest movie star in France - did a few times play in American movies set in France (including playing Porthos, IRRC, in the awful version of The Men with the Iron Mask Di Caprio was playing the King in), and though he's French, he was cast to play Christopher Colombus in 1492 (in which that casting is considered part of what ruined that movie), and a few other roles in Hollywoodian "period" movies shot in English. It never worked (obviously, aside from the American movies where he played a French character among American characters, like Green Card, that's very different), not the least because he's virtually the only actor playing with a big French accent.

It's not really what I meant, though. I meant filming the whole movie in French and using subtitles. Which of course, Hollywood would never do (at best they do it to an extent when a movie is set in a foreign country, but with American characters - as long as there's not all that much dialogue or they find some device around that, like having most of the foreign characters know English. A concrete example would be Last Samurai).

I know English speakers (and most non-French speakers) don't give a crap (why should they?). I meant that the convention of pretending English is actually French (or German, or whatever), or that American actors are French or German or Italians just doesn't work for a native from those cultures, and that's why personally I just can't watch those movies and I don't bother. It's especially bad in period movies, as most American actors don't have the cultural background for it, and you end up with massive differences in the ways they pretend to be, say, XVIIth century French people.

European movies (often) do this differently. It's far more frequent to hear many languages in European films (even big "commercial" movies) or for a director of one nationality to go film his movie in another country with actors from the country the movie is set in. The Americans rarely do. And I don't say they should, those movies would be big flops in the US.