Yes, the keyboard is compatible with the 4th generation iPad Air (2020). Logitech lists the Combo Touch as suitable for the iPad Air 11" of the 4th and 5th generation.

No, you'll probably have to ask Logitech. They probably also need a bit of time to adapt their products to the changes in the changing apples.

The "Combo Touch" keyboard for iPad is available in several languages, but I don't have any specific information about the language of the "DE" model you mentioned. However, Logitech generally offers keyboards in various language layouts, such as Qwerty or Azerty, depending on the region and model. For more details, I recommend that you consult Logitech's official website or check the product specifications directly on the packaging or in the documentation supplied with the keyboard.