I have heard this song since I was a child and believed it to be about a baby being taken by the fairies. One never praised a baby for its beauty in case the fairies took it. This has been said to be a reason for the highlander's lack of overt emmotion and understatement. I still think the 'sounds' heard in the chorus are far older than the given Gaelic chorus and probably go back as far as the belief in fairies itself. I don't know the word 'hò-bhan' to mean 'alas' and there doesn't seem to be any Gaelig words beginning with H, except where aspirated. So I believe the Gaelic chorus was made up to suit the traditional sounds. It's only a belief and that's why I was looking for the opinion of a Gaelic scholar ... no offence Wolfgang! but my Gaelic has waned somewhat (my German is now better!)
Slan,
Jim