Interesting. I think "pio" is the onomatopoeia for tweet in Japanese too. It's the noise cash registers at Tokyo's Inageya supermarkets make when you use their points card.

And in French "piou piou" can be used colloquially to mean "bird"... Many languages seem to agree on this.

In Hungarian, "pee-pee-pee-pee" is used to at farms to call chicken. :) And sometimes, young woman are called "pee-pee"-s, in a playful way.