Hey, thanks for the review!
Sorry about that, and glad that this is the biggest problem with the extension for you 😉

By default browser extensions simply follow the browser's locale. Changing that would require re-implementation of the internationalization API on my part, which I think is not worth doing on a per-extension basis. Rather browsers should provide a way to change extensions' language.

If you know Polish and have a spare hour, you can fix the situation by translating the English strings to Polish: https://hosted.weblate.org/engage/jump-cutter/-/pl/
I'll include your contributions into the next release, and your name will appear on "Extension Options -> License -> Translations LICENSE_NOTICES".

After you've done that, don't forget to rate your work by editing the review here 😃