I talked to the PayPal Merchant support in Germany and they told me that Website Payment Standard is available in Germany and they have no idea why Magento2 does not offer it in Germany. In Magento 1, its possible to use Payment Standard by the way.
PayPal Express is not always a solution because this Payment Gateway does not support downloadable and virtual products.
Workaround: Switch the country to a country which allows PayPal Website Payment Standard (Austria for example), configure the Payment method and switch the country back to Germany. The settings for Website Paymwent Standard in the Magento2 Backend will not show any more, but the payment method is working in the frontend.