You really need to find a course first and then enquire at the respective universities about admissions criteria. It varies a lot depending on institution (whether Fachhochschule or Universität) and Bundesland. I think it could be a waste of time doing A Levels unless you want to go to a Fachhochschule (applied university) because they are normally regarded as a Fachabi and not as an Allgemeine Hochschulreife because the breadth of subjects is too narrow, and then the Fachabi would have to relate to a course at a Fachhochschule. IB would thus be better. It is not possible to be admitted to a German university without some form of Abitur unless you in some cases you have a certain amount of professional experience or have done an Ausbildung. Although it's inflexbile in that way, an Allgemeine Hochschulreife (which you can nachholen at a Kolleg/Abendgymnasium - google "der Zweite Bildungsweg"), once gained, is a golden ticket. Unlike in Britain, many university courses even at prestigious universities, have no Numerus Clausus (oder "nicht-zulassungsbeschränkt), which means anyone with an Abi can sign up a couple of months' before the beginning of the semester and start in September.
It may be different in other regions but in Bavaria this is your option:
- zwei Jahre Berufstätigkeit to qualify for state Kolleg/Abendgymnasium
- ein Jahr Vorbereitungskurs (unless you've done German at Mittlere Reife level, which if not educated in Germany/Austria/Switzerland, you won't have done) at state Kolleg/Abendgymnasium
- 2-3 years for Abitur at Kolleg/Abendgymnasium
- Can start at university
6 years just to get to the stage of being able to go to uni?!
I'd seriously think about your desire to study at a German university before proceeding.