on language code.
 Both options accepts a list (comma separated) of country code(2/3 letters)
or name (english/native).
 For demuxers that doesn't provide language info, they are ignored.

 Support for dvdnav isn't complete (only first language is tried) and untested.

 Ex: --spu-language en,fr will try to select english track and if none
 then french one (and if none, no subtitle).
 (you can also use --spu-language english,french or english,francais)