I am using 'i3` window manager on Fedora 25. I've already uninstalled GNOME Desktop. I want to change keyboard layout and set it to languages other than English, and desirably also to set it as Alt+Shift shortcut for easy access.
You can use setxkbmap:
setxkbmap -layout us,de setxkbmap -option 'grp:alt_shift_toggle'
Just change the keyboard layouts us,de to what ever you prefer. If you want i3 to run these commands on startup, just add them to your config file "~/.i3/config" and prepend "exec".
exec "setxkbmap -layout us,de" exec "setxkbmap -option 'grp:alt_shift_toggle'"
It indeed seems that everything must be written inside a single command in the i3 config file in order for setxkbmap to work as desired, at least on Arch linux.
Example: English + Czech qwerty keyboard, ALT+SHIFT toggle:
exec "setxkbmap -option 'grp:alt_shift_toggle' -layout us,cz -variant ,qwerty"
"exec setxkbmap" didn't work for me. Through frustrated keyboard smashing, I accidentally pulled up the display settings (Super+D since I installed from Regolith-desktop), and from there I could open up "Region & Language" to set the keyboard layout. I guess i3 "Ubuntu" keyboard layout settings are store separate from "Kubuntu" keyboard layout settings.