There are problems when songs in minority languages get translated, I fear - more so than when songs in majority languages are translated. This leads to further erosion of cultural and linguistic identities. Minority languages need to be heard more, not less. This is especially true in the home countries of those languages. More specifically as in this instance, Welsh needs all the help it can get!

Artistically, it's also pretty much impossible to capture the true spirit, meanings and subtleties of many songs in another language, in my experience. So much is lost. Some of the Victorian translations of Welsh songs are awful, for example. I'd prefer the song to be sung in the original language and a literal, prose translation given if necessary.

Better, then, perhaps, to do as seems to have been done by the Mormon Tabernacle Choir above, and write new words which aren't an attempt at a close translation (although they keep to the theme)