Not long ago, Thomas Quasthoff started a recital with a ramble about why he was singing Mussorgsky's Songs and Dances of Death in German. Since that cycle is standard repertoire for bass baritone someone had better tell all the other guys who've been singing it in Russian for years! Specifically, TQ singled out Robert Holl who had sung it and the even more demanding Shostakovich Michelangelo songs the previous week. Holl doesn't speak Russian as far as I know, but he was apparently extremely good (as one would expect from a singer of his stature). So why the fuss ? So much for TQ's theory. Here is a clip of TQ singing in English.
And then a clip of Paul Robeson singing the same song. It's so deeply felt. "Ol' Man River...what does he care if the land ain't free...." This is visceral, powerful. It's much deeper than what's just in the words, a whole lot more than a cute tune.
"Let me go way from the Missisippi, let me go way from white man boss". That's what the song means : "Ol' Man River, he must know something but he don't say nothing". Robeson is the real article. Singing has a lot less to do with language than with conviction.
For more on Paul Robeson's remarkable achievements and troubled, persecuted life, see Roger Thomas's review of Martin Bauml Duberman's magnificent and definitive 804 page biography: Paul Robeson. First published in 1989, this was reissued as a paperback in 2007. See http://www.alcala.demon.co.uk/robeson.pdf