TRANSLATIONS!
Translating this extension is actually pretty easy, see: https://i2pgit.org/idk/I2P-in-Private-Browsing-Mode-Firefox/-/commit/e08ce1c71e2a2c3f38dbfe063fb4c3436b64cb0e
The translations themselves are just JSON files located in _locales/LANG/messages.json, as demonstrated in the crude Spanish translation in the checkin above.
This is also an issue for tracking issues with translations in general including awkward phrasing, missing tags, and un-translated messages. These should all be discovered in the next day or two as translating highlights their visibility.