The native name of Tai Viet script and language(s)

[Eli Zaretskii via Unicode]

> Date: Tue, 27 Aug 2019 08:33:21 +0100
> From: Richard Wordingham via Unicode <unicode at unicode.org>
> 
> @Eli: Ideally, you need to check that default font and language are
> consistent.  There are some regional differences which make it
> necessary to calibrate the writing system, and one word may not suffice.

Emacs doesn't yet have a useful notion of "the default language".  It
is a problematic notion in a multilingual editor anyway.  We do have a
mechanism in place to prefer some fonts over others give "the current
language", though, see fontset.el.

Specifically, for this context, I'd be glad to have the right text in
the Tai Viet script in _any_ of the languages that use this script, as
those greetings in the HELLO file are just a kind of show-off.