On second thought, since Campbell was part of the "Irish Revival" period, and for a time changed his name to a gaelicized form, he may have written a Gaelic translation of the poem. Here is what John McLoughlin wrote to me when he first sent the third verse:

Hughes collected the trad melody in Donegal (of which I am a native) the previous year and Campbell wrote the lyrics. His other best known song is of course "My Lagan Love". He dropped the Irish form of his name after hearing someone call him Sam McCatwail !!