One thing that bothers me is that mIRC doesn't support Unicode. As such, people may only communicate in a few languages that use Latin-1 encoding. I cannot type even a few words in Russian, without resorting to translitteration, i.e. using Latin characters for equivalent Russian ones (which is hard to read and even to write, as some characters have no equivalent -- Russian alphabet has 32 letters, while English has 26).
This will benefit everyone who wishes to use a different language that is not Latin-based, or has special characters not in the Latin-1 character set.
(If this feature is already available, and I just didn't find it, please tell me.)