Never mind that he says "wan wan" in Japanese, we've already run into problems where the dog says "woof" in one book and "bow wow" in another.
Now we can turn this problem into a game of its own, with Bzzzpeek.com, which is a collection of recordings of children from over 17 countries making the onomatopoeia sounds of animals, machines, vehicles, and other stuff in their native languages. It was produced by FL@33, a London communications firm.
Bzzzpeek.com [flex33.com, via Travelers Diagram]
I don't know if you are familiar with the Tintin books, but they were originally written in French (the author is/was Belgian) and have been translated into a bunch of languages.
Being a bilingual household (French and English) I look forward to the day when we will have copies in both languages in the house. I don't look forward to explaining to my son why guns sound different in both languages or, more importantly, why certain characters have completely different names. There are twin detectives in the books and in English they are Thompson and Thompson, in French they are Dupont and Dupont. It will be very confusing I would guess.
In German, the frog says "quack"; for reasons unbeknownst to me, the duck does not say "ribbit".