It's specially weird considering how you can send stuff like áíéúóàâêôãõç in the Japanese client even if it's not rendered but can't in the "global" client. You literally can't send the name of the étoile class or some of the clothing items of the latest AC scratch like Escuridão or Oscurità in the chat. You can type it, the font renders it, you can search for it on the market, but you can't send it on chat.
No error sound or anything, doesn't even deactivate the chat window like it does when you successfully send a message or command. (When not using direct chat, that is.) Doesn't seem like a bug but deliberate. If you can send it through macro then it isn't a proper blacklist either.
Absolutely mind boggling.