We are tentatively intending to work on adding easier, more complete and officially-supported localizations for the cart sometime later this year. At the moment, the cart display is only available with text labels in English, although there is a javascript technique to replace some of the text labels and buttons with custom text, which can be in any language you wish. Let's see... that would only work for basically anything in the lower half of the cart, under the itemized order details, such as Update Cart, Continue Shopping, Ship to Country, Ship to Zip/Postal Code, and Discount Code.
PayPal Pro is only available for Sellers in the US and UK; we hear that Canada and Australia may be available soon, but we have not heard anything about PayPal Pro for Germany or EU. However, a regular PayPal standard/business/premier account will still work fine for a Seller based in Germany. If you are selling Tangible Goods -- or at least enable the Shipping option for your products (even if you won't charge any extra for shipping) -- then whatever country the buyer selects in their cart should determine the language of PayPal's checkout pages for them, and once they log into PayPal to approve payment, their own PayPal account's language setting determines the localization they see after login.
