Can't add needed locale

The docs say:

It is not possible to create custom locales. Locales can only be created based on the 500+ pre-created list of locales set by Strapi.

I just need to supply content in a locale that is not listed. Is there a way to extend that list to add my needed locale? Why does the locale need to be added to that list? Why is adding a custom locale limited to only the ones Strapi has written down and not all languages/locales?

I’m just forking the plugin for now, but seems like an unnecessary limitation.