Hello Mike,
I found it and it is a embarrassing ….
I found out that a designer set the caption at the backend.
WooCommerce -> settings -> Tax (german: Mehrwertsteuer) -> standard texts (german: Standards?tze) -> you can set for different countrys different taxes. And here you can set a controlname (german: Steuername)…
Here the designer set the name of the control on “Regel” what later show at the cart.
That was the problem.
So it is solved and problem still no more.