Welcome to Eorzea!

Sadly, having played on a JP server myself in the past for an extended period (on the same data centre as you in fact, but on a different server, namely Ridill), I can honestly say it is very hard to do - the language barrier will be a problem, especially when it comes to roleplaying. So much so, that even though we had a few JP friends in our FC (and they were very nice and friendly), my friends and family ultimately decided that it was just too difficult to continue on Ridill and so we transferred to Balmung (the unofficial English-language RP server) at the end of 2014, where we have been ever since, and we have had a much easier and enjoyable time. But ultimately it is up to you.

Either way, good luck!