I have never had a problem with JP players. I've had it explained to me that they normally don't want EN in their pt for the reason that our play style is different. I really couldn't say what the difference is since the parties that I've had were on BLM.
I actually have a lot of fun with the JP players outside of party. I usually just do something weird and they would play along.
I never used proper JP etiquette with them, but I have been very polite with them. In return they have talked to me for a bit with what english they do know. I had one JP actually help me with Bastok missions and we chatted for hours doing 4 missions. She had explained that they were mainly set in their ways from family teachings growing up to not appreciate Americans.