Actually, dual citizenship in Germany is only allowed for a few select non-EU countries. For everyone else: first you apply for citizenship. Then they say citizenship will be granted, under the condition that you provide proof of revoking your previous citizenship within 2 years. Then you revoke your previous citizenship and give the confirmation to the immigration department. They will process it (during those weeks you are practically stateless) and grant you citizenship on this basis. Source: did this three years ago