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 the localization is sourced here. If you fix more than a few lines of an existing language, or provide a new language, I'll give you a license key for Middle.
Not all text in each file needs to be translated. You only need to translate what's seen by the user, and this is in the Master.strings file. A lot of the existing translations include a bunch of menu items that aren't visible to the user.
Translations can also be emailed to support@middleclick.app instead of updated via GitHub.
Translations for any languages that aren't localized at all are also welcome.
The viewer is a visualization of what the app sees from the touch data it obtains. Hold the option key in the menu bar icon menu to see this in the "Debug" menu item.
If you select three finger click as the trackpad gesture, this checkbox will appear. It's basically just a way to pan using the trackpad since you can't move it around with mouse click down like an actual mouse.
All of those messages show if you have the three finger drag option set in macOS System Preferences before you set three finger tap/click for trackpad.