Tclkit has always been distributed with only a few Unicode encoding definition files in it. This was a compromise to reduce the executable size (from 1.4 Mb to 1 Mb) yet be good enough for many common Western languages.
That does not do justice to other parts of the world, so here are instructions on how to create a modified Tclkit with all encodings Tcl knows about.
You will need three things:
The encodings can be obtained from a Tcl source code download (unpack and look in the library/encoding/ directory).
Below is a transcript (on Linux) of the steps needed to add all encodings:
I assume that similar steps are also what would be needed on Windows.