As far as the forum goes, that's up to UBB to choose to support, so that's not a mIRC bug or even mIRC related. You should feature request it on their forums.
And there are complicated issues with having the scripts editor support unicode because it can cause scripts to be broken when moving them between people who have and don't have unicode enabled. I'm sure that will be added at some point, but it's not a bug.
For the rest, I don't use unicode, so I can't really help you there. Someone else can probably help with that.
