Adding Spanish audio to movies

Hi there thanks in advance for any help. My family doesnt speak much english so i was wondering if there is a way to add a spanish audio file. i know how to add the spanish subtitles using MKVmerge Is there anything like that i can do for the audio also? Thanks for any help.
Answer #1
Mkvmerge will add more audio tracks. Click add just like you do for sub tracks.
Answer #2
do you know where i can find spanish audio for movies