A Sheumais --
Tog go bog e!
Let's leave the linguistics out of it. As Percy French once said, English may not be the old language, but it's the one we all know.
Mind you, I do sing in a couple of kinds of Gaelic, but I've translated a lot of verses into English just so people in my area will be able to understand them. But onstage, in workshops and in the liner notes of my trio's CD, I also encourage people to learn the originals once they've wrapped their heads around the concept.   
Those Barbie dolls on PBS were not Queen Medb, granted. I would have called the show "Irish Cuties Warble 4U" or something. For some nice *real* Celtic stuff, check out Barbary Grant's CD's -- songs in English, Irish, Scottish, Manx, & Welsh; clairseach (yep -- real wire strings); and both ancient and modern sources. (She has a website somewhere.)
Now we just have to convince PBS to put someone like her on, in addition to the Cuties.