This is quite normal. Your font probably doesn't have the "åäö" characters. With font linking enabled, mIRC is searching through your fonts for those characters from another font that can be used instead. It hangs the first time while it searches through the list.
You can either use a font that properly supports unicode or disable font linking. Disabling font linking will mean you won't see the characters, though.
Okey, that makes sense, can you recommend one that does support UTF-8 with åäö? im currently using
courier new.