Very interesting. The team behind Ancestris, the genealogy app I highlighted yesterday, have developed a tool named Trancestris to help translate the resource files used by Ancestris.
Trancestris is, itself, a NetBeans Platform application too. Apparently, it is very easy to use it, and it is available for Windows, Mac OSX, and Linux users.
Would be extremely interesting to find out whether this tool could be used generically, e.g., to translate NetBeans IDE, for example, or any other application created on the NetBeans Platform. From the screenshot, it would appear that one registers a ZIP file containing sources of a NetBeans Platform application and that then all the bundle files are exposed. A nice task for someone to investigate would be to take a look at this and try it out with a ZIP containing the NetBeans sources!