One thing I've noticed with Japanese people (both those I've met with in RL and in game) is that while they may not speak and write English very well - MOST of them actually READ English VERY VERY well. It's required in many of their schools. So don't be talking about JP players in your party - chances are they will understand at least some of what you are talking about - and it won't make your JP partying exp any easier.
I was in a very good JP party last night for about 6 hours. We totally raked in the exp in Yhoator Jungle - and we were using 2 Warriors as Tanks - which is almost unheard of anymore, at least in most of the parties I've been in lately. Party setup was Thf (party leader and good friend of mine), Whm (me), Blm, Smn, War, War. Everyone but me and my friend were JP-only - and we did really well. The one problem we had was when our Summoner somehow aggro'd an Ivory Lizard (still have NO idea how that happened - probably a mis-target) died on the way to the zone, I went to raise him - and the lizzie went back and killed everyone else. >< Woops! Honest mistake on multiple parts (I place the blame on me, but nobody else did ^^) but thankfully I didn't die so I was able to raise everybody.
Everyone got at least 2 levels - one person got 3, and then the THF and BLM left, I was leader, and I replaced them with NIN (JP)and BLM(NA), and we had a great time getting lots more exp, until everyone was just ready to leave.
So with the use of Autotranslate and patience and understanding, I was able to get the JP Nin to join our party, and we had a lot of fun. Although I was a bit worried that our Galka War was saying mean things about me since I didn't understand what he was saying...until he started pulling when my friend left and I realized he was using his pulling macro on me! ^^
Amanada is right though - learning ANY other language (I speak English and Russian myself) really makes you a lot more tolerant and patient with language barriers. That goes for EVERYBODY no matter where you live. JP players should learn another language if they don't know one, NA players should learn some...etc etc. Speaking Russian has actually gained me some really good friends in FFXI lol. SO - yeah...I'm done.