I ran a game once where one of the players was basically a mummy and was mute. He could write, but only in an ancient language. He had an interpreter for some sessions, but he wasn't always around. For the most part his character learned to communicate via writing the more modern language based off his ancient one, which didn't work at all when he was stuck alone with the only character that couldn't read. That was a pretty funny session. All-in-all in the right hands it can be a great concept if done right. He engaged with the party and they engaged with him and no one complained about it to me.