"iok" is not a very helpful menu entry. "Indic Onscreen Keyboard" is much better. 
A simple way to get there is to pass the --copy-generic-name-to-name option to desktop-file-install.

While looking at the desktop file, Icon=iok.png  will give you a warning from desktop-file-install. The correct way to specify the icon is to strip the extension: Icon=iok.

The comment "Indic onscreen virtual keyboard for Indic Inscript maps." has some flaws:
- it ends with a period
- it repeats Indic
- it repeats the generic name, more or less
A better comment might be:
"Enter Indic characters with a virtual keyboard"