I am writing here because I found out some problems related to the use of UTF-8.
mIRC fails to save correctly the logs of channels having UTF-8 characters in their name: in the filename there are the single-byte characters. Anyway, it is still possible to see correctly the logs using a UTF-8-compatible editor.
mIRC shows on the main bar (and other bars, too) the single-bytes characters of channels formed using multi-byte characters. It could be a problem from the operating system, though, I still need to dig it out.
Sometimes, multi-byte characters are shown as single-byte ones by moving the nicklist.
UTF-8 is not supported in the scripts. At all.
UTF-8 is not fully supported by this forum, neither.