English: "moo"

Estonian: "mop"

Finnish: "muu," "ammuu" (Courtesy of Jope)

French: "meug, meugle"

German: "Muh" (Courtesy of ba)

Greek: "mu" (Just kidding)

Hebrew: moo (Courtesy of undone.)

Hungarian: "mú" (Courtesy of ba)

Japanese: "moh"

Norwegian: "Mø" (Courtesy of Sverre)

Polish: "Yazooo"

Portuguese: "múúú" (Courtesy of e-anorexia)

Spanish: "muu"

Swedish: "muuu" (Courtesy of rollo)

please /msg p_i with further contributions to this (or other aspects to noises animals make in different languages), assuredly the best use yet found for the global forum that is the Internet.