My previous experience with RP on different region servers like that was on the Persistent World mod for Mount and Blade: Warband. There were Hardcore Roleplay servers for EU and NA. I played both but in my humble, worth nothing opinion, the NA RP was better by far. It had nothing to do with language that i noticed, just willingness in the community to engage in it.
EU servers were way more hostile and sometimes RP was basically just a few words to provoke a fight or a war. NA server on the other hand had more people playing deep characters and even non-violent pure RP type characters etc.