In Vim, the usual way to jump to the definition of the keyword under the cursor is to type CTRL-] (as claimed by :he CTRL-\]).
But when you have a QWERTZ keyboard (see below, Strg is Ctrl), you're in some trouble: there is no separate ] key on the keyboard; you'll have to press ALT GR-9 to type the ]. So, to jump to a tag, it`s neccessary to hit CTRL-ALT GR-9 which doesn't work (and is also not feasible because you'll break your fingers if you happen to use that often).

So, how could I jump to a tag using my QWERTZ keyboard?
In addition, I'd also be glad if someone could explain why pressing CTRL-ALT GR-9 does not work.
Edit:
I'm not interested in the obvious answers "remap to something else" or "press the mouse button".
Duplicate on Vi/Vim: https://vi.stackexchange.com/questions/5732/tag-navigation-using-ctrl-does-not-work-with-non-english-keyboard-on-windows