I've been doing this since forever. Hell, playing with players from different regions is one of the biggest reasons I started learning to speak and read Japanese and German years ago. About the only excuse a person has in a group is if they're either French, or an asshole.

But really, the auto-translate function is a great tool for that sort of thing, unless you need to get really detailed about specifics. Most of the Japanese players I play with don't really speak very much anyway, so the point is moot. Just join the duty finder on all languages. This game was designed to be a cross-regional game like FFXI anyway.