Actually, some movies are in a language none of the actors speak. An example would be the recent Crouching Tiger, Hidden Dragon, which was in Mandarin. However, only one of the actors spoke Mandarin, so the remaining actors had to learn Mandarin. And they did. Thus, there is a 4th, very long and hard way to get around the problem.
Update: A reader informed me that the accents the actors use are, apparently, hysterically bad. Still, it's impressive anyways...