I use Cmd+[ on MacOS to "go back" on multiple software like IntelliJ, emacs (I probably configured it) and Firefox, so I would say this is a pretty common combo. It's easy to remember, specially given that the mirror, "go forward", is Cmd+]. As I said, even though my first language is not English, I only write code in an English keyboard layout so I've never even considered that [ is "hard to press".
EDIT: the Dr Racket editor even lets you write Lisp using '[' and ']' because they don't require pressing shift like '(' and ')' so are easier to press.
Using [ and ] is completely normal in so many applications. QWERTZ just is a bad design, and applications shouldn’t have to work around that by making keybindings more difficult. My team has ~100 engineers in QWERTZ countries and I don’t know a single one of them that actually uses it. QWERTY is the standard order for all new laptops. Nobody complains.
EDIT: the Dr Racket editor even lets you write Lisp using '[' and ']' because they don't require pressing shift like '(' and ')' so are easier to press.