Localization delivers 33% extra players. Or, to put it another way… at least a third of game players are not speaking your language.
Game localization - general information about localizing games.
Internationalization - information for programmers. A table details some of the major issues addressed by internationalization.
Blood & Gore - Cultural and legal issues for designers. Wealth warning: cultural and legal issues can seriously damage your game.
Whatever level of localization you require, you should send an email to firstname.lastname@example.org first!