@MovR0R1 said:
Language codes vs. region
Hi,
great to see you provide a forum for question.
Thanks in advance for any answers, and I hope I am not too confusing

Question:
I am somewhat confused by the language / region difference and mainly how the language parameter can or should be specified.

I advise using ISO-639-1 + ISO-3166-1, the language and the country.

I see that the default for the language parameter is 1. 1. en-US.
However, when I use the languages endpoint (https://developer.themoviedb.org/reference/configuration-languages),
I only get a list of two-letter language codes (en, de, ...), as expected from ISO-639-1.

Maybe this list will help.
https://developer.themoviedb.org/reference/configuration-primary-translations

What effect does the region part in the language code have?

Some time ago users asked to add the country because despite the same language the local title was different.
For example pt-PT and pt-BR.
There are many films with different titles between Portugal and Brazil.
Furthermore, the language is the same but with several different word usage characteristics.
What impacts the Overview.
See the list in the link above for the various countries with the same language.
And some countries with multiple languages.
India, for example, has 5 languages, I think.
Canada has 2 languages, English and French.

Today images only receive the language.
It is planned to use language-COUNTRY.

And can I make a valid API request using only the two-letter language code?

If you use only the language you will receive the default Language-Country data (title, overview).
In the case of pt you will receive pt-PT, from Portugal.
I believe that in the case of en you will receive it from en-US, from the USA.
And if I remember correctly, in some Requests it can cause some problems.

My use case comes from validating language and region codes in my application before sending them.
I could validate language and region separately and then combine them, but this would allow non-existing combinations like pl-US etc.

Can I just send the two-letter language code, and the region parameter separately, would this affect the response?

I don't think so.
An API Request must contain the parameter.
I don't know how to split the parameter into two parts in the same API Request.
There is a separate Region parameter but, if I remember correctly, it affects specific cases like premiere dates.

And if not, is there and way I can get the list of these combined codes like "en-US" for validation?

In the link I posted above.
https://developer.themoviedb.org/reference/configuration-primary-translations
I don't think this list covers all the language-COUNTRY options in the world.
But it should solve 98% of the problems.

What we have in lists today:

• 187 Languages
• 251 Countries
• 140 Primary Translations