As part of Heimdal 1.3 we have been adding i18n support to the base libraries and some of the Kerberos user utilites using GNU Gettext. It should also work with other localization packages like the MacOS X CoreFoundation's CFCopyLocalizedString with some minor code hacking.
We that work on Heimdal only know Swedish and English, so can can help translate the error strings. You don't need to download special tool, just go to Heimdal at launchpad and you translate the strings there. Just let us know that you have started to do the work so that we will remember to download your translations before release (or when you want to sync to you can test how it feels to get heimdal in your language.