Earlier quoted context omitted.
If you have trouble hitting [ how do you ever program anything? I use multi-language keyboard layouts and switch all the time... when coding (or using "hacker" software like this, which is completely based on emacs [and as far as I know is written in Common Lisp], not vim), just use a layout that makes it easier (in my case, en-AU).
Entering [ works just fine on QWERTZ: You simply press AltGr+8. But this doesn't work in shortcuts, e.g. when combined with Ctrl. That is, AltGr+8 generates the character '[', but Ctrl+AltGr+8 is not the same as pressing Ctrl+[ on keyboards that have a dedicated [ key. This bug is decades old, and every Vim derivative suffers from it.
If so, I'll try and remember that if ever tempted to use Ctrl and {[]} together I need to handle that as well.