An IB is a secondary school leaving certificate issued by the International Baccalaureate Organization (IBO). It serves as proof of the general university entrance qualification.
The IB is considered a non-Austrian school leaving certificate (even if the exams have been taken at a school in Austria), but it is considered equivalent and therefore no nostrification is necessary, provided that certain criteria are fulfilled.
As opposed to holders of other non-EU/EEA secondary school certificates, holders of an IB diploma do not have to prove the special entrance qualification (statement of admission).
German knowledge has to be proved. If you have a grade of German in your IB it can be accepted as sufficient proof of German knowlege.