well, here's my suggestion
i personally use 3 languages
English, Hebrew, and Russian
english and russian work perfectly fine for me
i can both type and read these in mirc
BUT, when it comes to hebrew, in order for me to see it
i have to switch the font of the channel/query window to Arial
and change its encoding to hebrew - only then i can read hebrew in the channels, and yet i cannot write. i get gibberish.
i hope you can help me solve my problem in the next mirc version

also i'd like to comment on the fact that up until either mirc6+ or 5.9, all 3 languages used to work for me. for both reading/writing (of course it stil required font switching, but thats fine with me i guess)