@seyman said:
get languages for listing?
Is there a way to fetch a list of all the language codes via the API?
I am looking to populate a drop-down list with all the languages and let user filter.

We have 3 different lists
In some cases the ISO 639-1 language code is used.
In other cases the ISO 3166-1 country code is used.
And in other cases the combination, language-COUNTRY, of the two codes.
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