Hi
User Troponin can help you, he speaks German,
community.getk2.org/profile/Troponin
Please go to K2 control panel, then categories, then open the category that you need to display intro text.
In the parameters in the right panel, you will see an option "introtext" then a field to enter word quantity.
That will help.
Please also check
simon.getk2.org for further k2 documentation I have written.
Regards,
Simon
K2 Support