Board Thread:General Discussion/@comment-1155842-20140425085530/@comment-1739368-20140425095936

Yes, It's heavily implied in Part 3 that all of the group speaks fluent English. This becomes apparent when Joseph screws up the order when trying to order in Japanese at the restaurant. He doesn't seem to be well-versed in Japanese at all, which presumably means the rest of the group has to speak in english in order to communicate with him.

On another note: It would be interesting to watch the anime in a different style, where they get voice actors of different ethnicities to act out certain characters. Like the entirety of part 5 cast, for example, would have all italian voice actors and speak solely in Italian.