I am the author of the Send Later Thunderbird add-on (here on BabelZilla), which allows users to schedule email messages to be sent at a later date. Send Later has over 67,000 active users, and is translated into 15 languages.
I haven't released a new version of the add-on requiring translation updates in quite a while, and unfortunately my translation team has "entropied" a bit and some of the translators have not responded to my recent request for an update.
In particular, I am in need of help updating the following translations: de, fr, ja-JP, pl, pt-BR, sv-SE, zh-CN, and zh-TW.
If you are able to help, please PM me or just join the translation team for the language(s) you can help with. Obviously, you can also PM me if you have any questions about the strings that need to be translated.
Thanks very much!