Joomla Templates - German umlauts ö, ä, ü, ß are not displayed correctly

The installation package was not changed. It was installed with only the German Joomla language file. The website does not have this error. the error appears only when I want to open a category from the directory. 

Sorry for my bad english 

The error in Pictures: 

Homepage here: 

As I have seen on demos of the reservation, in this demo, this problem occurs. It will therefore probably some people may be affected. Unfortunately, I find in the forum to no solution. So I can not use the tamplate and directory.