Tim -- It looks like Hyfrydol is the tune usually used now for Wesley's words. I have Protheroe's 1918 hymnal, he uses the tune, Gaerwen, but then uses Ann Griffith's unrelated words, Rhyfedd, rhyfedd gan angylion, for the Welsh. In the US, we don't now sing any of Wesley's words to Hyfrydol. So, it look like the Welsh never got around to paraphrasing Wesley's words into Welsh. But maybe someone else can help on this.

My primary interest is finding carols that I can do on guitar, so I'm not looking for anything too heavy. And especially anything recent with a nice folky flavor.

Thanks for all the help I got on this from all the good people here, as always,
Nadolig llawen yn gynnar iawn, Chris