I have created a separate project for calibre plugins translation. If you send me a message on transifex with the names of the plugins you want to create translations for, I will create the entries in the Transifex database and make you maintainer for those resources, so you can upload pot files, download po files etc. The project is assigned to the calibre translation team, so existing calibre translators can easily contribute to the translations.
https://www.transifex.com/projects/p/calibre-plugins/