@warrenbeattystan said:
Adding Nahuatl to language options
Would it be possible to add the indigenous Nahuatl language to the language options? The 1944 film MARIA CANDELARIA has spoken Nahuatl but there is no way to add this to the entry. I'm sure there are other examples of this group of languages being used in other films because it is currently spoken by millions of people.

language-Country

I believe that the language/Country you want or suggest is not part of the ISO 639-1/ISO 3166-1 list.
It is only part of ISO 639-3. https://iso639-3.sil.org/code/nci
Therefore, it is still not possible to fulfill your request.
See below how TMDb manages languages and countries.

TMDb uses ISO standards to identify Languages and Countries.
ISO 639-1 alpha 2 for Languages. Standard with 184 Languages.
This standard assigns 2 lowercase letters for each language.
https://en.wikipedia.org/wiki/List_of_ISO_639-1_codes
ISO 3166-1 alpha 2 for Countries. Standard with 239 Countries
This standard assigns 2 capital letters for each country.
https://en.wikipedia.org/wiki/ISO_3166-1
Example:

en-US = english-United States
fr-CA = french-Canada
pt-BR = portuguese-Brazil
hi-IN = hindi-India
zh-CN = chinese-China

And there is a list of language-countries supported by TMDb.
You can make an API request to obtain these lists.
https://developers.themoviedb.org/3/configuration/get-languages