How can I ask a German university for a deadline extension ?
Try to figure out who the actual person working on your application is (often, there will be a web page detailing who processes applications, based on the applicants initial of the family name). Then send an email to that person, or call him/her - in many cases, mails will be likely to be preferred, as they do not disturb the workflow as much as a call. Briefly explain your problem, what materials are still incomplete, and when you expect you will receive them. Ask whether this is critical, or whether you can hand them in after the deadline - and also if there is something else you can hand in instead. For example, if you will not receive your final diploma in time, perhaps a statement from the exam office that you have finished you degree may be enough to carry you over the deadline. In general, these questions are easier to answer if we know what university you are referring to - but of course, you are then likely to get less answers (not my university, I dont know how they handle things). Good luck with your application!