I have successfully built a German localized build of the PR1.0 source code. These localizations are not official and do not represent the final localized version(s). All builds found on the page below should be considered experimental and for use in testing environments only.
You can find the localized versions here:
http://www.moox.ws/tech/mozilla/localizedbuilds.htm
Please test them out and let me know what you think, of any shortcomings, etc...
Cheers,
-Moox
MMx_edit: adjusted title