Some of the problems I have seen in the past are:
1. Non English spam blocking the majority of players chat messages. (see OP screenshot)
2. One game started having lag problems from the use of multiple text fonts
3. Adding in the multitudes of fonts somehow opened a backdoor allowing players to game the game (not sure how it worked)
4. Snowball effect...where does it stop? Each and every language in the world will want their own, try policing all the languages of the world at once in a mmo.
5. It will alienate non English speakers even more, eventually possibly turning into an "us versus them"
Also think about trying to translate all the training information into different languages, plus the key commands, etc etc. I understand trying to add a more varied playerbase and thats always a good thing, but a line has to be drawn somewhere. I played a German based MMO, and I attempted to learn some German, just to try and stay competitive. I didn't ask them to cater to me, so why should this game cater to non English speakers? Imagine hearing German,English,Italian,Japanese,Cantonese,Russian, etc all at once on vox. Adding a forum section...who will police it? Or will it be ok to bypass rule #4 if the mods can't translate the post correctly?