Describing Guimarães Rosa as a "Brazilian James Joyce" is a bit inaccurate. While James Joyce
intended to emulate the workings of the mind
with his distortions of language, Guimarães Rosa attempts to add the oral elements of the marvelous and largely uncharted dialect used by the Brazilian lower class to his stories. Sure, both are wonderful, but they are different kinds of manipulations. It resembles more closely what José Saramago
accomplished with his books based on oral tradition.
That said, Guimarães Rosa was skilled in a huge number of languages, and that leaves traces nearly all of his works. His first book, for example, is called Sagarana, a fusion of the word "Saga", as should be familiar to English speakers, and "rana", marker for collective in the native Brazilian Tupi language.
Translating Guimarães Rosa should be about as hard as translating Finnegans Wake (a work which is being translated to Portuguese by Donaldo Schuler, by the way), but without all the critical apparatus that was built around Joyce's works over the years, and without the relative familiarity of the Irish culture. Even to most urban Brazilians, Irish culture is probably more familiar than the rural areas Guimarães Rosa portrays.