You may or may not have heard about the DownThemAll! 4 - WebExtension Edition beta I am currently doing.
I released a "lite" WebExtension version of DownThemAll!. See https://www.downthemall.org/
The WebExtension is localizable, but I don't think babelzilla supports such translations.
So if you'd like to contribute a translation nonetheless, have a look at our translation guide at: https://github.com/downthemall/downthemall/blob/master/_locales/Readme.md
Essentially I set up a small self-contained, no-registration-required website somewhat similar to a very basic WTS where you can translate stuff. If you use that one, make generous use of the Download button in case it is buggy and loses some of your work. Of course, you can use your favorite text editor instead, as well.
The translations can be directly loaded into a running version of the extension including the latest signed beta release (but the beta had some stuff not translated yet, so some things might not show up as translated in there, even tho the strings are there).
Right now we have the en and de locales already, with a pl and a fr locale forthcoming.
If you have any questions or get stuck on something, let me know, either here, or in a github issue (I will probably check the latter more often).
Thanks for your help in advance!