This paper intends to provide a thorough survey of the multi-faceted claims described in Franz Rosenzweig’s translation theory. A paradoxal axiomatic proposal of his is the notion that there is only one language and, therefore, that this assumption is vindicated in each and every language used by human beings. This stance is tested by the careful scrutiny of manifold observations provided by Rosenzweig in his own work as a translator of Jehuda Halevi’s Diwan and in his collaboration with Martin Buber in a Verdeutschung of the Hebrew Bible. The whole range of this speculative endeavour should be read against the seminal intuitions on the art of translations, whose operation is finally conceived as a vector of redemption, a redeeming drive of the One language.