Hm, yes, the only languages for which UTF-8 is compatible with the old encodings are those which only use the letters A-Z, primarily English.
For all other languages, everyone needs to be able to at least read the same character sets.
One way to make this happen is to ensure that everyone on Windows uses mIRC 6.17 and has UTF-8 on. The alternative is for everyone to use the old encodings, but this in turn creates compatibility problems between languages and between users of Windows and Linux/Mac OS X.
I can only say that I hope people will try Unicode out... It's quite handy once one gets used to it!