I believe Miranda IM has a patch available for UTF-8 support. At least some versions of Trillian/Trillian Pro support it too. As far as I know Visual IRC is not particularly popular, even if it is there hasn't been a release since
January 2004. Given that it's open source if there hasn't been a new version in over three years I think it's fair to say that it's not very popular and that it's possible there may not even be another version.
Which leaves IRCle. Which is the only one of the four that is a major client really. A quick check of the
version history shows that as of February 2006 Unicode/UTF-8 support is planned "for the very near future". So I guess it should be available soon. Then again if you read the IRCle forums you'll see Onno said that UTF-8 would be supported "later this year" in a post from August 2004.
I have no idea if any IRC bots handle Unicode/UTF-8. Believe me when I say I couldn't care less about them.
The UTF-8 encoding matches ASCII for codepage values 0-127 (ie. control chars, a-z, A-Z, 0-9, all common punctuation), so if you chat in English you won't notice the difference.
