Basically it's a good idea. But the reason why it only takes place in the German forum is support. The contest isn't there just for fun, but to learn by creating own solutions and learn from others. Most people who take part in it can talk best in their native language. That's why it's "limited" to the German forum.
If anyone of you wants to take part, go for it! Would love to see you around.
And btw, the reason I show the entries here is to show other people what's possible with SFML with just a plenty of time and resources. Maybe it at least enhances the portfolio a bit and gives also Laurent some feedback on his great library.