That would depend upon whether the emphasis is on the tongue or the music and it would appear that it's the tongue here.

It's pretty rare, although not unknown, for any non-English lyrics to make the top 40 in the UK, especially if there are no English lyrics at all.

My memory comes up with French as the most successful tongue (Dominque, Je T'aime and nothing comes to mind in a Celtic tongue at all.

Even Runrig who have had a chart success, didn't succeed with a Gaelic song.

I wouldn't be too hopeful alas.