This workd on my LinuxMint desktop. This might work on Debian based all distros.

sudo apt-get install ibus ibus-m17n m17n-db ibus-gtk
ibus-daemon -xdr
setxkbmap
Menu> System Settings> Preferences> Input Method> Input method> IBus
IBus Preferences > Input Method > Add > Sanskrit > ITRN
reboot

To Switch Language Input

  1. Ibus preferences
  2. Keyborad Shortcuts …. click dots on the right
  3. Select the mofifier key
  4. add key code
  5. hit apply and okay

You can also add and delete key shortcuts.

Add ibus to system start-up list

Install gnome start-up UI

sudo apt install gnome-startup-applications

Launch start-up UI

gnome-session-properties

add ibus to system startup programs’ list and save and reboot the system.

add ibus to system startup programs' list and save and reboot the system