[PP-1] Add tests and document how to include translations in recipes

I think a test would help define how to include translations.

For this we're testing enabling translations and adding config of different languages to the config folder and verifying that it imports it correctly, yes?

That should be a great place to start!

In attempting to create a test for this I found that the RecipeConfigInstaller doesn't process translations, which is to say that if you put language files in config/language/[langcode], it ignores that config. I'll create a new issue for that and leave this one here for creating documentation once that's fixed.

Postponed on #3453331: RecipeConfigInstaller should process translation config files →