By the way, further to Matt Milton's post, in which he wrote: "and that Bob Marley song you mention Johnny Cash covering: I bet Cash doesn't pronounce "they" as "dey" the way Marley does."

Cash makes absolutely no attempt to do a Jamaican accent - he just sings in his own accent. So given that, of course he couldn't say "de" for "the" - that would be stupid.

It seems to be a general rule that American and Canadian singers make to attempt to sing folk songs from elsewhere in the originating accent. I think that's a shame, personally. I've often wished that Joan Baez would desist from singing Scottish folk songs, as I think they sound stilted in an American accent. But British and European singers do generally try to imitate the accent of the country a song comes from, and as I say, most British singers sing even their own songs in an American accent.