[tex-hyphen] synonyms for language identifiers (for Arthur Reutenauer)

[Arthur Reutenauer]

> It would be easier to set up \setmainlanguage{en-GB} ;-). I’m not a
> programer, so the same variable could be passed without conversion.

  I take it these identifiers would come from pandoc?  Where are they
set?

> I will open an issue in polyglossia.

  I didn't mean now ...  As said I am aware of the issue, it's been on
my radar for a long time.  But it is quite a bit of work, and I want to
do it right.

	Arthur