fbxkb is a freedesktop.org NETWM compliant keyboard indicator and switcher. It shows a flag of current keyboard in a systray/panel area and allows you to switch to another one.

Install an appropriate software package-
fbxkb-0.4 PET thread (non autostart)
fbxkb-0.4 PET post (autostart)
fbxkb-1.0 PET post (autostart)

How To Add/Change Keyboard Layout
Input Device Index - more input options
Language Support Index

fbxkb homepage
fbxkb-0.4 Country keyboard indicator thread
Add extra language keyboard layout, switchable
NETWM - freedesktop.org spec