Letter of application
You can write your application in German or English, depending on which language you feel more comfortable with. We usually don't need a cover letter from you if your resume indicates why you are our perfect match. It helps us if you not only list your professional stations, but also describe your concrete activities and responsibilities as precisely as possible.
By the way: If you have already entered all this information in your XING profile, we will only need a simple link to it instead of a CV.