It's a common problem, not a lot of people get this right. When I boot with lang=ru cheatcode, /etc/init.d/knoppix-autoconfig automatically selects xkeyboard=ru, too. The problem is that to get any work done I still need to go to keyboard layout settings, add 'us' keyboard and select some switchng hotkey (it's impossible to type commands or URIs with 'ru' layout, you'll get ыуечлиьфз -щзешщт пкзЖсекд_ыршае_ещппду гыбкг and реезЖ..лтщззшчютуе. instead). It's not a grave problem in Knoppix (not only I can add xkeyboard=us to boot parameters, there is even a GUI to setup layouts), but it can be solved completely in different ways:

1) Add another cheatcode which would set XKBOPTIONS in /etc/default/keyboard, so it would be possible to boot like this: knoppix lang=ru xkeyboard=us,ru xkbopts=grp:ctrl_shift_toggle
2) Copy the logic from, for example, d-i (https://sources.debian.net/src/conso...n.config/#L487): they first set the layout[s] based on the locale, adding 'us' if needed, then add -option grp:alt_shift_toggle,grp_led:scroll if there is more than one layout (also, lv3:ralt_switch if the layout is single, but non-US).

Best regards,