After 7 weeks, my traffic on the new domain dropped from 100% till 10%. During this time, my overall site traffic (the other languages) increased by 15%. I see no error in webmaster tools and I am not aware of any.
I keep on thinking on what tedster said and I can not understand what is the difference between what he did and what I did. The only thing that comes into my mind is that... this language was never really promoted, so it has very few incoming links. Can it be that all it's power was provided by the main site and when I moved the pages, they lost it all?