Wikipedo says:
The word “meow” is onomatopoeic. Different languages have correspondingly different words for the “nyan” sound, including “miau” (Belarusian, Finnish, Lithuanian, German, Polish, Russian, Portuguese, Romanian, Malay and Spanish), “niau” (Ukrainian), “niaou” (νιάου[4], Greek), “miaou” (French), “nya” (ニャ, Japanese), “miao” (å–µ, Chinese (Mandarin), Italian), “miav/miao” or “mjav/mjau” (Danish/Norwegian), “mjá” (Icelandic), “ya-ong” (야옹, Korean) and “meo-meo” (Vietnamese)