Localized strings are spread in many .properties files, but I made a tool that gathers all the .properties files in one big file to help translators.
The size of this file is 37 KB at this time.

Please note also that translators should translate also the 4 main web pages of Sweet Home 3D (home page, download page, documentation page and import furniture page).
If possible, I would prefer also that they translate the help pages because a good software should have a localized help system (and this avoids also future help requests of users).

If you're still interested, just answer on this forum, then, I'll send you the required files.