Here's why everyone should try your best to get the first release versions of Diamond and Pearl in Japanese:
Gamefaqs' forum on Diamond and Pearl explains a way to get Darkrai and Sheimi WITHOUT using an event, by exploiting an in-game programming glitch. Nintendo recently found out about this, and they're working on new editions of Diamond and Pearl that fix this problem. Plus you can bet your DS that the American release will not contain this glitch. So, this is your only chance to get a "legit" Darkrai and Sheimi, other than visiting a Nintendo event (which is practically impossible for some of us).