Well, adding language specific servers would just just another fail decision regarding the game. All region/language-based MMOs already reflected that when you do this you end having a "useful" period on that server (peak period) and anyone that plays out of that period ends in a major disvantage...and, if someone that wants to play with japanese-speaking people is forced to move from japanese-speaking server due the lack of player online during the period he plays, then the language-speciific server loses its purpose.

I support the global servers concept! IMO it's good for the server health, to keep population at a decent amount the entire day and even for cultural interaction! I myself am a person that very often play overnight/morning, staying at JP and EU periods most of the time even though the "correct" server for me would be the NA/english one.