If you mean support for communicating in other languages, mIRC can do that already. However, mIRC can only use the internal systemwide encoding that Windows uses, so that means that to speak in Chinese, for instance, you need to change your Windows settings so that Windows uses Chinese. The Japanese don't even use the same encoding that Windows does, so that's why there's an option called "SJIS/JIS conversion".
I recommend that you search for the phrase "unicode" or "UTF-8" on this forum and see what I and others have said about the UTF-8 encoding. The UTF-8 encoding can support a wide variety of languages with virtually no fuzz, except for some font problems with Asian languages, and a lack of Asian characters in older implementations. UTF-8 is what's used in Mac OS X and Java.
(One of the threads has a reply from Khaled where he says it's on his todo list... He's got a cute avatar.)
If you mean localized versions of mIRC for the benefit of non-English-speaking users, there is a page dedicated to that here:
http://www.mirc.co.uk/translations/index.htmlHappy hunting.