Much thanks, but now how do I install it?

Just run:
cpan -i Tk
Duh ... the source needs to be altered, doesn't it :-(

Download https://cpan.metacpan.org/authors/id/S/SR/SREZIC/Tk-804.035.tar.gz
cd to your local directory in which Tk-804.035.tar.gz resides.
Run: tar zxvf Tk-804.035.tar.gz
Run: cd Tk-804.035
Make the changes to encGlue.c specified in the earlier part of this thread.
Run: perl Makefile.PL
Run:  gmake test
Run: gmake install

Cheers,
Rob