[NTG-context] Adding built-in support for Serbian language

[Henri Menke]

> (PS: I would say that adding support for transliteration of the text
> from one script to the other would be a really nice feature. Then you
> could type your text for a book once and have it typeset in both
> versions without any extra effort :)

There is Philipp Gesang's transliterator package:
https://gitlab.com/phgsng/transliterator
https://modules.contextgarden.net/cgi-bin/module.cgi/ruid=199735311/action=view/id=50

Cheers, Henri