After posting the previous report about keyboard hotkeys in menus, I decided to investigate further to see what was involved with keyboard input.
I noticed that when "Learn" is set to On, and some key combinations are pressed, the resulting characters show what would (presumably) be key names on the German keyboard layout:
To get those 4, I've pressed, in order:
Ctrl+` (back apostrophe, left of "1" key on standard 101 keyboard
Ctrl+\ (backslash, above enter key)
Ctrl+[ (these two should need no explanation)
Ctrl+]
There are probably others.