Cart – checkout where to change language

Hello guys,
https://hausplaner-24.com

Having worked on the language file (I put the one from DT45 into ST45) I translated everything.
In the checkout area ist still “Step 1: Checkout options”, “Your Delivery Details” etc. I cannot find this string in the language_deutsch.php, neither is it in the main-menue/general settings/language area.
Where can i change it?

By the way – the dropdown below, where i can sort in my question into this forum, doesnt show Responsive-Themes=>ShopperTheme (so i put it into DT45)
Thank you, best regards, Daniela