Robert Heinlein wrote a novel that begins as follows:
"Easy, boy, easy."
Don Harvey reigned in the fat little cow pony. Ordinarily Lazy lived up to his name; today he seemed to want to go places.
Heinz Nagel translated it as follows:
»Ruhig Blut, Junge, ruhig Blut.«
Don Harvey zügelte sein strammes kleines Pony. Gewöhnlich machte Lazy (was zu gut deutsch Faulpelz heißt) seinem Namen alle Ehre, aber heute schien er es eilig su haben.
The phrase "zu gut deutsch" has a certain superficial appearance of being a prepositional phrase, but we don't see a dative form of the adjective "gut"; indeed it seems to be getting used as an adverb, and "deutsch" does not have a capital initial letter.
Can someone explain the syntax here?