Middle is a macOS app that's made specifically to provide middle click functionality to the Apple Magic Mouse and trackpads.
The app is closed source, but here are the localization files. It's obvious that I've used machines for the translations. If you fix more than a few lines of translations, I will give you a free license for the app (or a refund if you've already purchased it).
Keep in mind that a lot of the strings in those files are not used, as I left the base menu in the app. It's only necessary to fix localizations that are actually displayed in the app.
Translations can also be emailed to support@middleclick.app instead of updated via GitHub.