Set Layout

Set layout to British English.

setxkbmap -layout gb

Or Polish with:

setxkbmap -layout pl

Language	short
Polish	pl
Serbian	rs

Set 'alt + shift', as the command which cycles through the British English, Polish and Serbian keyboard layout.

setxkbmap -layout gb,pl,rs -option grp:alt_shift_toggle

Alt_GR

Remap, e.g., the right Windows key, to Alt_Gr.

    key <RWIN> {[  ISO_Level3_Shift    ]};