ISO 639-1 language codes. See https://en.wikipedia.org/wiki/ISO_639.
There are about 8000 possibilities, and it causes performance issues for the Elm compiler, editor tooling, elm-format, and the Elm doc site if I generate all of those options.
The Language codes that I've included in this module represent the majority of common cases, and together with the ExtendedLanguage values, you can build most of what you want.
For everything else, there's LanguageTag.custom as an escape hatch (or open an issue to share your use case).
Get the ISO 639 language code value for this Language.