Vic has a good argument there.

On the other hand, the Irish and English languages have co-existed in Ireland for several centuries, albeit for much of the time not at all harmoniously. Quite a few songs in Irish have been translated into English and we might expect some to have gone the other way. So perhaps a ballad in Irish deserves to be included if it looks like a translation from a Child ballad, but not if it looks like an independent telling of the same story, and not if it tells a related but different story.

Then again, "a related but different story" applies to some versions in English.

My two penn'orth!