I'm on windows 7 x64. I've tried to paste Japanese characters on Windows Vista 32/64bit and it didn't work. I have the japanese language packs installed but it doesn't seem I can paste any characters at all; katakana, hiragana and kanji.
Not all characters will show up in the edit box, though once mIRC's fully unicode, that will likely change. However, you can still paste it and it will send to the channel. Whether or not it gets sent correctly to the channel and whether or not it displays correctly on your screen depends on your mIRC settings as well as your font. And whether or not someone else can see it even if it's sent correctly will depend on THEIR settings and font.
Note that language packs aren't required to paste and/or display Japanese characters in mIRC.
You need to have the right font. mIRC will do its best to font-link any missing glyphs, but if your font is fixedsys you'll get the best results if you switch to a proper unicode font. You should try Arial Unicode MS, which has one of the larger sets of unicode symbols.
are there, maybe, any free alternatives for a font with full unicode support? buying a license for mIRC broke my bank (and heart). unless the font is like 1USD, i couldn't pay for it.