gxkb is a little indicator applet which allows to quickly switch between
different X11 keyboard layouts.  A flag corresponding to the country of
the active layout is shown in the system tray area.

The applet is written in C and uses just the GTK+ library, not any other
GNOME components, and can maintain separate per-window, per-application,
or global layout states.

WWW: https://zen-tools.github.io/gxkb/