[Karnagious]

Cant do much about the variable subtitle selection without a tonne of more work, but here is a service that does some of what you talked about.

https://github.com/KODeKarnage/service.native.tongue

The first thing is does when you start playing something is switch off the subtitles. It will then check the audio streams for what you are playing. If it recognises one as your preferred language, it changes to that audiostream. If it cant find one in your language, then it switch on subtitles.

It defaults to English, so dont forget to set your language in the Settings.