@unknownuser2567 said:
Add language - Hmong
Is there any way to add language option for Hmong, currently unlisted

language-COUNTRY

I believe that the language/Country you want or suggest is not part of the ISO 639-1 / ISO 3166-1 list.
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.
get/configuration/primary_translations
https://developers.themoviedb.org/3/configuration/get-primary-translations
https://api.themoviedb.org/3/configuration/primary_translations?api_key=THE_KEY
get/configuration/languages
https://developers.themoviedb.org/3/configuration/get-languages
https://api.themoviedb.org/3/configuration/languages?api_key=THE_KEY
get/configuration/countries
https://developers.themoviedb.org/3/configuration/get-countries
https://api.themoviedb.org/3/configuration/countries?api_key=THE_KEY

Indeed, at this time we use the ISO-639-1 standard which does not have Hmong as a valid language. It doesn't look like this language was added to the standards list until ISO 639-2.