There is a streaming platform Rakuten Viki (quite popular among Korean drama lovers) which already has a language learning tools as a part of the product. I haven't used it personally because they are focusing on Korean, which is not my language choice, but it looked quite nice.

Also they have a subtitling community - any user can contribute to shows translation.

I am struggling to understand why Netflix is not thinking about that. It would greatly improve the experience and, probably, user base too.