Yeah, that helped. I was confused because it says: "Show action text" and than i also have the option to Displace (something).
The only problem is and i guess that's not very user friendly: if i want the text to be shown at the bottom-center, i have to show the background of the scene as a background image to place the Textarea in the right position and after that i have to delete the background again so that it will not override the scene. But ...
... here comes the big "but" ... when the background of my scene is larger than my chosen resolution, (so that the picture will slide to both sides when my character moves from one side to another) i have to "guess" where the perfect Textarea should be.
a) just use the global action text"rectangle" in the main game settings and let it "fill" a square at the bottom of your screen. Its always there, no extra interface needed. You dont need to use the display action text function inside the interfaces.
b) create a new interface with another interface class, dont forget to set it active for the character. In here activate the action text and draw a rectangle inside the interface at the bottom. Use placement "absolute" and a transparent (or even an image) as a background