Same thing with one of my sites. It ranks VERY good on .com and co.uk but on .de where it SHOULD rank good it is only on #7 or so. I noticed that this is caused by the hl= parameter in the url. When I set hl=de then my site ranks #7, when I set hl=en my site ranks #1 . Very sad because as my site is in german it is useful to germans ONLY. I wasn't able to figure out what Google makes think my site is more interesting to english-speaking users. I tried with meta language="de" but no effect. The only thing I can think of is links, but I still have more links from german sites than from english ones. Very cruel!