At birth abroad, children whose German parents or German parents were born abroad after 31.12.1999 and have/has their habitual residence abroad at the time of birth do not acquire german nationality by birth if they acquire a foreign nationality by birth.
Only if the parents apply to the competent registry office in Germany or to the competent German diplomatic mission in Germany within one year of the birth of the child in the birth register, the child acquires German nationality retroactively at the time of birth.
Example case of the German diplomatic missions abroad:
Mr A was transferred to Spain by his company in 1999. His daughter Klara was born there on 01.02.2000. The family returns to Germany after a few years. In 2018, Klara meets an American citizen with whom she moves to the UNITED States. Her son will be born there on January 1, 2020. Although his mother is German, he does not acquire German citizenship by birth, as he acquires US citizenship by birth in the USA.
In order for the child to acquire German nationality, Klara or the father of the child must submit an application to the competent registry office in Germany or the competent German diplomatic mission to declare the birth of their child. If the application is submitted in due time and in full, the child may be issued with a German passport upon request.
The German diplomatic missions point out that this regulation may affect all Germans (expats and emigrants) who were born abroad themselves and have a child abroad, regardless of the reason and duration of their stay abroad.