404 template in German? How and where can I define my own German text

I am using YOKO 1.2.1 and I want to make my own german 404 template. There seems to be one as there is german text shown. But I do not know how I can edit the various languages in YOKO theme.
When I go to the Design – Editor section, I can see all text in English.

How can I extend the Germen text outside the editor. Also I recognized that the Text style is then different. e.g. here
https://www.wunderbarehaut.de/?page_id=2485