Copy this to ~/Library/Application Support/DVD Player Scripts/12 Next Language.scpt
When called, the script will cycle one step through the available audio tracks, e.g. the next audio track.
Since apples DVD Player lacks a “choose audio track” menu, this does the trick.
OS version: OS X
tell application "DVD Player"
activate
set audioTrackMax to available audio tracks
set currentAudioTrack to audio track + 1
if currentAudioTrack > audioTrackMax then
set currentAudioTrack to 1
end if
set audio track to currentAudioTrack
end tell