I made the API Request.
https://api.themoviedb.org/3/discover/movie?api_key=[THE_KEY]&region=RU&sort_by=primary_release_date.desc&page=1&with_crew=1071
https://api.themoviedb.org/3/discover/movie?api_key=[THE_KEY]&sort_by=primary_release_date.desc&page=1&with_crew=1071

&sort_by=primary_release_date.desc
I compared the two results.
I went to check only the first two that are not included in the survey region=RU
https://www.themoviedb.org/movie/173228-something-necessary/edit?active_nav_item=release_information&language=en-US
https://www.themoviedb.org/movie/275772-rosakinder/edit?active_nav_item=release_information&language=en-US
Neither film was released in Russia.
I didn't check the others.

I have checked - those 26 movies mostly have Russian description (with adding language=ru-RU).

These two films that I checked only have pages in English and German.
They do not have a page in Russian.
You can provide the link for any of them that have a page in Russian, but it does not appear in the search region=RU?

I believe that if it was not released in Russia, or rather, if it does not have a release date in Russia registered here in our database,
then, it will not be included in the response to the Requisition that specifies discovering films by an actor or crew that has been released in Russia.

There is no need for the page in Russian.
There needs to be a release date in Russia.
The existence of a page in Russian does not change the answer.

Translated by Google

@ticao2 said:

I believe that if it was not released in Russia, or rather, if it does not have a release date in Russia registered here in our database, then, it will not be included in the response to the Requisition that specifies discovering films by an actor or crew that has been released in Russia.

Yes, this is the crux of it. If you specify region, it will filter items that have a release date for that region.

@ticao2 @travisbell thanks! Question can be closed.