I'm making myself a playlist of songs I like in different languages. I already have a lot of European language songs but am always looking for more.
For the UK I've got Ymaelodi Â'r Ymylon by the Super Furry Animals (Welsh), Tressor by Gweno (Cornish), Guise of Tough by Iona Fyfe (Scots) and Hùg Air A' Bhonaid Mhòir by Julie Fowlis (Scottish Gaelic). I've also got Dty Skeealyn by Biskee Brisht (Manx, not strictly part of the UK) and Íosa by the Cranberries (Irish, also spoken in Northern Ireland).
Update: For a list of all the languages and songs I've got so far (not all European), see the spreadsheet at Google Sheets. I personally listen to the playlist on Apple Music. However, there are also Spotify and YouTube versions (though they're each missing a couple of songs). To keep everything in sync, I prefer to update the lists from a computer, so it might be a few days before I add some of the great suggestions here.