If you are a German citizen born abroad after 31.12.1999, please take note of the following:
For children born abroad and whose German parent(s) was/were also born abroad after 31.12.1999, a registration of the birth in Germany must be requested within a year after childbirth in order for the child to acquire German citizenship, if the child already has already acquired another nationality at birth (§ 4 StAG).
For further information, please refer to point 3 of the information on acquiring German citizenship published by the German embassy in Berne (in German).