If I had to speculate, and thats all it is, a speculation, I would say there is a good chance that multilingual support will be in the next version of mIRC. I say this because, mIRC has a ton of messages to translate, that could certainly account for the 1+ years that it has been since the last release. I personally can't think of any other suggestions that would take such a long time to do. But like I said, it's just a guess.
