When opera singers sing folk songs it often seems that their priority is the musical sound rather than the sense of the song. That can apply to other singers, of course. That's why it often doesn't work too well.
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As has been pointed out, typically when Irish singers sing songs from other countries, they tend to make them sound Irish, and I think that's generally the right way to deal with songs from other countries.

What is a bit daft is when you have a song like that, which in fact comes from some other tradition, but is sung in Ireland, and they put on an Irish accent for the occasion. For example, Hard Times.