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
- Ibus preferences
- Keyborad Shortcuts …. click dots on the right
- Select the mofifier key
- add key code
- 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.
