Good question. I couldn't answer it immediately, so I've just installed etch on a spare machine, and gnome-terminal does the trick. Here's screencast of <ctrl><shift>20ac and <ctrl><shift>30db, which you can see turning into a euro symbol and the "Katakana letter ho":
http://www.sourceworks.co.uk/iso14755.ogvI've tried a "plain" xterm on the same machine, and it doesn't work.
I think it's time for me to have a chat with the gnome-terminal people...
J :-)