The following tools can make your life as a KDE translator a lot easier. Don't worry if you don't understand the feature listings on first sight. You will understand them as soon as you know how GUI and doc translation really work. I thought it would be better, however, to list all resources in one place than scatter little bits of information all over the document.
Apart from just using your favorite editor you have basically the following three options:
Ktranslator by Andrea Rizzi (KDE 1x only at the moment)
KBabel by Matthias Kiefer (KDE 2x only)
and the GNU Emacs PO module (po-mode.el) that comes with the GNU gettext package
Some features and advantages to using these specialized programs are listed in the appropriate section on GUI translation.
As for SGML handling there's apparently no better solution in free software yet than using (X)Emacs in SGML mode. (For people who are not that well-versed with Emacs, there are a few hints on setting it up for SGML in the doc section.). If LyX already supports DocBook (as it supports LinuxDoc, the former SGML standard in KDE) is presently under investigation. Any feedback on this subject is highly welcome.
Of course, there are quite a few non-free packages around. But for obvious reasons they can't be taken under consideration here. (BTW: For reasons unknown, the Linux version of Corel WordPerfect does not contain an SGML module like the Windows version does.)