Catalan:
"meu" (Courtesy of koala.)
Chinese: "mao" (Courtesy of BrainsOfSteel.)
Danish: "miav" (Courtesy of Carthag.)
Dutch: "miauw" (Courtesy of fuzzy and blue.)
English: "meow"
Finnish: "miau" (Courtesy of Jope.)
French: "miaou"
German: "Miau" (Courtesy of mawa.)
Greek: "naiou" (Courtesy of donnaidh_sidhe.)
Hebrew: "Miau" and sometimes "Miya" (Courtesy of undone.)
Hungarian: "miau" (Courtesy of ba.)
Japanese: "nyan", "nya", "n'yao" or "myah" (Courtesy of nekojin and tongpoo.)
Korean: "yaong" or "nyaong" (Courtesy of Provolo.)
Norwegian: "mjau" (Courtesy of delta.)
Portuguese: "miau" (Courtesy of e-anorexia.)
Spanish: "miau"
Swedish: "mjau" (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.