Not wanting to get fired, I asked a couple of questions. Would there be legal implications in blocking legitimate mail to and from workers based on the alphabet of a language? Would it cause problems to allow Juan to send mail in Spanish while not letting Tuan use Chinese? Finally I hinted that the mail filters might not be able to read HTML images well enough to determine what alphabet was being displayed.
I never got an answer.
Most mail servers, including Exchange (especially with some add-on products), can filter mail based on character set. But the real question is whether you should do so. If you need to work with other people in this big blue world, you might want to think through your filtering policy from a global, rather than knee-jerk, perspective.