1. Копируем файл 90-keyboard-layout.conf из /usr/share/X11/xorg.conf.d/ в /etc/X11/xorg.conf.d/

2. Смотрим варианты переключения клавиатуры:
grep "grp:.*toggle" /usr/share/X11/xkb/rules/base.lst

Выдаст примерно вот такой список:

  grp:toggle           Right Alt
  grp:lalt_toggle      Left Alt
  grp:caps_toggle      Caps Lock
  grp:shift_caps_toggle Shift+Caps Lock
  grp:alt_caps_toggle  Alt+Caps Lock
  grp:shifts_toggle    Both Shift keys together
  grp:alts_toggle      Both Alt keys together
  grp:ctrls_toggle     Both Ctrl keys together
  grp:ctrl_shift_toggle Ctrl+Shift
  grp:lctrl_lshift_toggle Left Ctrl+Left Shift
  grp:rctrl_rshift_toggle Right Ctrl+Right Shift
  grp:ctrl_alt_toggle  Alt+Ctrl
  grp:alt_shift_toggle Alt+Shift
  grp:lalt_lshift_toggle Left Alt+Left Shift
  grp:alt_space_toggle Alt+Space
  grp:menu_toggle      Menu
  grp:lwin_toggle      Left Win
  grp:win_space_toggle Win Key+Space
  grp:rwin_toggle      Right Win
  grp:lshift_toggle    Left Shift
  grp:rshift_toggle    Right Shift
  grp:lctrl_toggle     Left Ctrl
  grp:rctrl_toggle     Right Ctrl
  grp:sclk_toggle      Scroll Lock

Section "InputClass"
	Identifier "keyboard-all"
	MatchIsKeyboard "on"
	MatchDevicePath "/dev/input/event*"
	Driver "evdev"
	Option "XkbLayout" "us,ru"
	#Option "XkbVariant" ""
	Option "XkbOptions" "grp:ctrl_shift_toggle,terminate:ctrl_alt_bksp"
EndSection