@DatLag said:
Please add "original_tagline" to movie details
Taglines are language specific, so if the movie has a tagline in english but not in german for example, the tagline field is empty.
It would be nice to have a "original_tagline" field like "original_title" in the details API response.

I believe it would be the Fallback feature.

There are plans to add this feature.
It's already on Trello's To-Do list.
There is no implementation deadline.
If you want you can vote. More votes, faster. :-)
See here:
https://trello.com/c/UV1IGYfN/3-add-support-to-fallback-translation-queries