go-i18n fails on custom language codes

[n10v]

If user wants to have custom language code that aren't in Unicode CLDR (like at.yaml, dk.yaml, ch.yaml, gb.yaml, etc.), bundle.ParseTranslationFileBytes returns no language found in "dk.yaml".
I don't think that users should be limited only with CLDR languages. They can freely use language codes they want and it can be technically implemented.
Discussion: https://discuss.gohugo.io/t/i18n-country-codes-as-part-of-the-url/6881

[bep]

I agree. In Hugo we use this language code as part of the URL in a multisite setup, and I have always assumed that I could abuse this feature to make multisite setups of whatever term I want, even non-languages. And even if we do restrict it to languages, I don't see why go-i8n should stop me from creating my own custom language.

[nicksnyder]

This sounds reasonable to me and it probably isn't that difficult.

You might only need to export registerPluralSpec. Then during your application's initialization register whatever language ids you want.

[n10v]

You might only need to export registerPluralSpec. Then during your application's initialization register whatever language ids you want.

I have an idea to make it simpler and without exporting something. Hopefully it will work.

[n10v]

Related lines: https://github.com/nicksnyder/go-i18n/blob/master/i18n/language/language.go#L61-L63

[nicksnyder]

I merged #79 which exports Operands and RegisterPluralSpec. I think this should unblock you.