Enabling TextView to print custom language character(without system support)

Hi
I am a beginner in c# and gtk. I want to modify TextView widget in such a way that it print (in textbox obviously) keys of my language Urdu. As if I press 'a' it prints 'ا'. The same thing is done by one of my colleges in Windows.Forms with richtextbox and textbox controls. I have seen some windows.forms specific things in it so I cannot apply it as it to gtk. Plz guide me how can I achieve it. I have found a little clue about it here in monodoc. Plz refer me to some guide in this regard even it is not GTK# (but gtk obviously) so I may able to understand even the lang will not c#. Here is the textbox class modified for this purpose for windows.forms.
UrduTextBox.cs
Regards