Let's look at how to put flags in Mate. In other systems, the principle will be the same (small differences still exist).
So, first we need to prepare the appropriate directory, where the system will "look" in search of graphical files for indicators. In the terminal:
Next, in this directory we need to move, in fact, files with images of flags of countries. In latest versions of Linux Mint flags already in the system, but lie a little not where we need. Let's execute the command:
mkdir -p ~/.icons/flags
Now all we have to do is activate the setting. Run in the terminal:
ln -s /usr/share/iso-flag-png/* ~/.icons/flags
gsettings set org.mate.peripherals-keyboard-xkb.indicator show-flags "true"
It is as easy to disable the display of flags as it is to enable: it is enough to change a single argument in the command:
May the Force be with you,
gsettings set org.mate.peripherals-keyboard-xkb.indicator show-flags "false"