going to the settings and changing the shortcut under "typing" section, there is no way to add "alt" key , it only allow the "super" key combo.
i tried downloading gnome-tweaks tools and changing it from there, it worked , but only partially. now i can press alt+shift to go from language 1 to language 2, but i cannot click again to back to language 1. (on windows i could keep clicking alt and shift to keep going back and forth)
i tried downloading another app from the pre-installed software and tried to change it , same problem.
i tried some commands from the Ubunuto forum, still doesn't work.
td&lr : activate keyboard shortcut for changing layout using right alt and shift key.