which audio to keep

[wrecked4]

while backing up some dvd's i seen that there are some audio streams the same

AC-3 Stereo English
AC-3 5.1-ch English
AC-3..........French
AC-3..........Spanish
AC-3 Stereo English
AC-3 5.1-ch English

why is there two the same?
does it mater which one i keep?
thanks