Ubuntu 18.04. How to set language (keyboard layout) change to Ctrl+Shift? [duplicate]
Install Tweaks (package: gnome-tweaks). Then use Tweaks to set an alternative layout switcher.
The full sequence of actions would be: Ctrl+Alt+T
sudo apt-get install gnome-tweak-tool
gnome-tweaks
then in the window Keyboard&Mouse -> Additional Layout Options -> Switching to another layout