I love this movie and the music - I don't think all of it is Welsh though, but the Celtic countries frequently sing each other's songs. My favorite is the theme that's associated with Angharad and the preacher - "The Sixpence" also called "It is not the tear at this moment shed" - I think this is an Irish song by Moore.   I always catch my breath when they play this in the movie. I think there are also a couple of other points where the music sounds Irish, especially at the end of the scene when Mrs. Morgan tells all the village people who are greeting her after her convalescence to come in the house and eat.

What a magnificent movie! The music and beautiful singing is as much a character as any in the Morgan family.