Yes, there is still a problem to be solved, it just can't be solved by changing qwertz_fn_keys[] in the keyboard driver. @VaZso's summary is quite correct, that we will most likely need additional language-specific custom keymaps to make this work properly. We probably also need the ability to remap the six 'modifier' keys with dedicated GPIO lines (shift, ctrl, fn_l, F logo, alt, and fn_r), and this is not possible with the current custom keymap feature. However, we are making good progress towards adding support for that.