Correct, he's shouting in Czech. Instead of that yours I've he's shouting Já, simply meaning me. It doesn't really matter, especially if his team mates are used to it already, and I am sure they are, but it sounds strange lol.
Maybe I misheard it but I'm quite sure Petr Cech is shouting in Czech, during corners and free-kicks. The basic shouts but still. I am really disappointed by the crowds, I thought there would be much more fans.