WALK IN SHOE LEATHER

I'm translating a book in serbian language and I desperately need the meaning of the phrase
WALK IN SHOE LEATHER

I haven't heard that. Seems like I've heard something like, "The meanest man in shoe leather." Most men wear shoes of some sort so this man is the meanest of that large category.

ESC, your phrase is an updating of a Shakespeare quote: "as proper a man as ever trod upon neat's leather" [Julius Caesar, Scene 1] ("Neat" is an old word for "cow".) As you say, the phrase is an elaborate way of saying "as [mean/ proper/ whatever you like]as ever was".