Fernando Romeu's short study of Spanish and Catalan translations of
Huckleberry Finn has been online for years:

The Translation of American Varieties in Mark Twain's Adventures of
Huckleberry Finn
http://www.tinet.org/~fromeu/hucktrans.htm

He now teaches English but I think he did this while he was a student.

While looking up that article, I also found a reference to this one in the
Journal of Sociolinguistics:

Raphael Berthele. "Translating African-American Vernacular English into
German: The Problem of 'Jim' in Mark Twain's Huckleberry Finn."
Journal of Sociolinguistics 4:4 (Nov. 2000): 588-613. Abstract: Focuses
on the most important problem translators are faced with when
translating Mark Twain's "Huckleberry Finn" into German: how can the
speech of The African-American Jim be rendered? Examines both
orthographic and other linguistic strategies that have been used to
differentiate Jim's voice over the last hundred years.

Jim Zwick