I just updated SU and now I have the German version again. That sucks. I use the English version since version 2.0 and two years ago I accidentally installed the German version and now there seems no way to going back to English. Or is it?
Any other professional app I know allows to switch language, in most cases even during runtime.
(I found a hack, but that’s kind of patchy: I deleted the German language packages from the app, so it goes for default. But: really?)
Wonderful idea. But I don’t have an “Apps tab”… 
(That would have been too easy, wouldn’t it?)
I don’t know why my post appears in several topics, but hey! I found help!
BIG THANKS to MikeWayzovski!!
Close Sketchup,
Open Terminal, type:
defaults write com.sketchup.SketchUp.2021 AppleLanguages '("de")'
hit enter.
to change back, type:
defaults write com.sketchup.SketchUp.2021 AppleLanguages '("en-US")'
Use at own risk… 
if fiddling on the command line is to cryptic, you may want use the free ‘Language Switcher’ app (signed, x64) for doing the same with a GUI instead. Drag’nDrop SketchUp (or whatever else) on the app and check the option “Dauerhaft” (= permanent) if you wanna keep it beyond the session.
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