Just a workaround for the moment:

You can get the region data (english and native name) by using the /configuration/countries endpoint (https://developers.themoviedb.org/3/configuration/get-countries). CL is listed there.

(Note: The native_name key, which is part of the watch provider regions response, is also in the countries response above. The documentation on that page is - at it seems - not uptodate (many other Schemas and Examples aren't by the way))

Thanks vkay for the answer.

I think I'll keep using the same endpoint and filter out the regions that do not appear there in other searches. It feels more natural to use the dedicated endpoints, and that's ok if we miss out on some few regions.

You're welcome ;)

Just an idea depending on your use-case: As I assume the configuration region data isn't changing often (I'm not involved so I have no idea xD), you could save the configuration/regions response locally once in a while since the data of watch/providers/regions is basically the same (I mean the names to the country codes match in both endpoints). Then you could use that local data to get the native/English name directly.