I was attempting, but failed miserably, to make the point that many old songs may have 'filler' verses to 'pad' out that song, or may include nonsense strings, such as fo-de-rol, dumble-dum-dooery, la-la-la.., etc. Often some word might be a mondegreen, a misheard lyric, or the same meaning in different wording. Some songs even have words mispronounced 'on purpose' in order to rhyme, or to allow the line to scan.
But, back to the Gaelic songs and non-gaelic singers... I allow them the same leeway as American singers trying to sing English songs, English people trying to sing 'country&western', and anyone who is willing to put themselves up there in order to practice the 'folk' art.
If you want to throw your teddy out of the pram because the song isn't linguistically perfect, why not keep quiet, and just think..'this rendition makes mine sound better'. and clap them for taking part.