Its been quite a long time, but now I am happy to announce that localized nightly builds have returned. The main intent for these builds are to help localizers check if their language changes are correct, but of course anyone can use them.
These builds are just in time for the major release of Lightning 2.6 which will be compatible with the Thunderbird 24 release. After the upcoming merge on June 24th, Lightning 2.6 will be on comm-aurora. If you are a localizer, please take the time to make sure your translations are accurate and ready for the release. If you are a user you can do the same, please report bugs in translation to the Mozilla Localizations product.