Add support for ISO 639 (639-1, 639-2/T, 639-2/B) codes used to classify languages

[ChristopherJHart]

It could be useful to have ISO 639-based language codes added as types in this project. I wouldn't mind working on a PR to add this in, assuming the team agrees it'd be valuable.

Thank you!

Selected Assignee: @adriangb

[adriangb]

That sounds reasonable to me. My only suggestion before you start work is that I'd rather they be Literals and not an enum if it makes sense to do it that way.

[yezz123]

Hello @adriangb @ChristopherJHart

Already @07pepa opened a PR regarding this and using literal as @adriangb recommends but what I notice is that already we can use pycountry to build this #141 (comment)