Können ich in der Schweiz mieten und dann selbst nach Deutschland fahren und dort zurückgeben ?

You can, but the cost of returning the car to a foreign country is relatively expensive, and there will be a fee for returning the car to a different location. Let me give you some information: It is generally cheapest to return a rental car to the same location where it was rented overseas, while returning it to a different location within the same country will be more expensive. Of course, the most expensive option is returning the car to a different country, and it will be significantly more expensive.