With 2020.2, its relatively easy to switch. You can go to system Preferences, Language and region, choose app tab and add SketchUp to the list. Set the language, there and (re)start SketchUp.
All langages are built in, except maybe Czech
Part of it is why the installer for Mac ‘weighs’ +700Mb, whereas the Windows installer only 208Mb…
not with macOS v10.14 ‘Mojave’ because this feature was introduced with macOS 10.15 ‘Catalina’ first… but SU 2021 claims to be compatible with macOS v10.14 upwards.