Two Languages: One ISO-639-# code

l10n
#1

All:

In testing out various grammar and spell checkers, I've come across a
couple of instances, where different languages/dialects share the same
ISO code.

IOW:
The _current_ ISO 639-1, ISO 639-2, ISO 639-3, ISO 639-4, ISO 639-5, and
ISO 639-6 codes are the same. They do have different Glottolog Codes.

The only solutions I found from Google searches were:
* Use "User-1" for one language, "User-2" for the other language;
* Use a completely different language and locale for one language;

The issue with "User-#", is that it is no longer found in standard
LibreOffice builds.

The issue with "use a completely different language", is that that
results in a language collision, when a user has to use both languages.

Question:
* What is the recommended practice for this type of situation.