The commentary includes all the phrases pronounced by the commentators of the game and it is different for each language. One of the most common jobs is to create the player call for new players but, with a microphone and a little bit of patience, you could insert your own comments or create a completely new commentary for a new language.
With Sound Master you can edit:
-the stadium effects
-the sound tracks
The stadium effects, shortly identified as chants, include not only the chants of the supporters but also national anthems and effects of the stadium speaker. Here yo can add more chants for your preferred team, there are many collections of chants available on the net for the most important teams, or you can record your own chant from a live game and import it in FIFA. You can also add the anthem for the new National teams you create.