In order to use an external audio file I use the same approach as to using an external subtitle, e.g I have the below in the same movie folder Name.of.my.movie.mkv Name.of.my.movie.swe.srt - for a Swedish subtitle Name.of.my.movie.deu.mka - for a German audio track Then I can use a different audio track with the same mkv, it's one of those great Kodi features