I like doomweasel's point. After all, we have characters not just from our own various countries (France, Japan, American, etc) but characters from different worlds & universes... who all miraculously understand each other ;)

Personally I've refrained from the use of Japanese honourifics, even though I want to call Tseng Sempai, Rufus Shachou & my nameless Before Crisis sister ne-san. Mainly because most of the other Turks have so far been very US-English that it seemed out of place :p