Unfortunately we already know the information the German participant provided isn’t entirely correct, as the Portuguese, Danish and Swedish decks do not exist. I guess he was very young at the time, so he just mentioned some of the countries where the other kids were from, assuming they received decks in their native languages (which wasn’t the case as they received an English one).
I’ve found a Japanese website detailing some more information. I’ll post a screenshot with some auto translated text.
Here’s the link to the Japanese website in case you were interested: pokeboon.com/jp/promo_event/pokemon-card-world-battle-in-hawaii/?fbclid=IwAR0686Ql3so6kVhL9S6KitYjwpw-wD_HxuamZm2f1M867umhWWMRH6Wh6rg
According to this link there was an Italian participant indeed. Also this source outlines the languages of the decks. Dutch isn’t mentioned so I guess we could cross that one out as well, which seems plausible.
I still wonder if the Italian, German and French decks were printed again in 2002 but that information is nowhere to be found