In Swiss German it does sound like Fee derrehh. Reminds me of the way wilander pronounces Eedbeargh, in Svedish. I always liked the South Effrrigen Lord cliffy Drysdale's way of pronouncing eedbewg.
Back to RF...
I am Surprised the Frenchies do not say rozhay fedèré, and they say fedair air....which sounds more Spanish.
French Canadians at the dépanneur prolly go avec Fedeureur.
Non rhotic Anglo: fedra
Murican: fedr fer shur.
Czech-Slovak, Indo-Pak and Serbo-Hrvatski: Federer. I think these guys have it right.