there are several packages available that provide tools and/or libs for
converting to and from rfc349 IDNs.
The following are all one of GPL, LGPL or BSD(ish?):
http://sv.gnu.org/projects/libidn (which requires
http://sv.gnu.org/projects/gengetopt to compile)
(the next versions of icu will also have idn support)
gentoo should have at least one of those in portage; probably all three.
libidn (and gengetopt) are basic econf && emake && einstall packages.
idnkit as well (but check out configure --help)
IDNSDK is a java package....
there is also a python package in libidn's contrib dir.
libidn is now in portage
I am not sure this belongs to this "bug#. However it would be very nice if the BIND ebuild would enable the IDN support. Check bug http://bugs.gentoo.org/show_bug.cgi?id=48610
In the portage tree already.