Set default subtitle language

At the moment no default subtitle language is set. This means that it is unclear with which subtitle language a movie is being played. In the attachment can be seen that "Track 5" is being used, which results in some Slavic non-English language for that particular movie.

Since the default interface is in English, VLC should have default subtitle language set to "en" (English). In the attachment this indicated with purple.

Implementing this would set a default subtitle language to a controlled value rather then let it be some language for which it is unclear for the user why that language has been chosen. Fixing this would introduce a stable choice of default subtitle language and increased user satisfaction.