It shows up as English on my computer. I thought the author was Dutch, so it showing up in German for you is possibly a little odd. I've been using it for a number of years. No problems to speak of. Incredibly helpful and easy to use.
the chicken calculator is helpful, a good learning tool, and really fun to play around with when your bored, but I do think it needs some refinement... better illustrations, or even photos( like on the duck version), of colors... the little icons at times leave a lot to the imagination... and not everybody understands genetics(the advanced genetics stuff on the calculator is a little imposing to the uninitiated, or even to those like me with only a basic understanding of genetics), so having the genotype and specific gene selection in an "advanced" mode, and a "basic", phenotype only mode for those who find that a little daunting.... the basic mode might realistically only be good for one, maybe two generations depending on the crosses, but it would be less "scary" to some people...