One thing I can't fault OS X on is fonts. The availability of good fonts with japanese glyphs is so far ahead of anything available for FreeBSD/Linux its not funny.
Ircle is going to have to go I think. While I was able to get it working properly in japanese (preferences and font issues), it has the annoying habit of going into japanese IM by default when its window goes into focus whenever japanese display is enabled. Xchat is probably next thing on the list to try.