[Ace]

The easiest way would be if XBMC could pick up local subtitles while scanning and adding them to the stream details. I won't add a check for local files because that's too slow and would need an extra db.

There's a PR from pieh which deals with the recognition of ext. subs' language : https://github.com/xbmc/xbmc/pull/1365 .
I opened a PR at pieh's repo to store this info in the db some time ago. But I have never heard anything from him.