Okay, this is a bit tricky.
The Easy Way
You could simply type in IRSSI:
/SET term_charset utf-8
The Hard Way
If things doesn't go the easy way, take a look at this.
Install FriBiDi and HebXFonts. Now, the next part is a kind of an academic guess: It might involve some path altering in the Makefile of HebXFonts.
As for me, I did all of the above until it just worked.
Good luck.
konzepz
2009-09-24 00:59:21