That's fascinating, I didn't realize that key serves multilingual support in some countries. Is that the standard configuration in China or a common setting for that key there?
It's been the macOS default for a few yeas. Before that, we usually assign Cmd+Space for this (in Windows it was Ctrl+Space for switching language and Shift for toggling between English and Chinese). Then Siri came so the combo stopped working. Possibly it was then when Caps Locks became the default.