It doesn't bother me that American actors usually don't affect foreign accents when portraying Europeans. If you think about it, the characters in this movie are actually conversing in French but all of the dialogue is "translated" for the viewer's benefit. Affecting provincial or national European accents distracts more than enhances the narrative in films made for English speaking audience, IMHO.
One such example can be seen in Grand Hotel (1932), where the entire story is set in a post WWI Berlin hotel. All of the actors except Greta Garbo are Americans playing Germans; only one of those Americans, Wallace Beery, bothers putting on a German accent. While I think Beery actually did quite well in his delivery, it certainly clashes with that of the rest of the cast (with the exception, of course, of the Swedish Miss Garbo.)
Okay folks, show's over, nothing to see here!