How to get list of available transcripts as the website sees it

[Bluscream]

I want make a simple function that fetches the transcripts that the website would see when you click on the "options" -> "subtitles" setting in the player, i think these are all the manual ones + 1 auto translated for the user's ui language, right? How would i make a method for that + have it as optimized as possible (aka only using minimal time waiting for responses and not double requesting stuff)