Which authority in Germany is responsible for you depends on which Land (federal state) you are resident in, so it is best to ask your municipal or district authorities or foreigners authority.
The citizenship authority responsible for people who do not have their habitual abode in Germany is the Federal Office of Administration, a subordinate agency of the Federal Ministry of the Interior (www.bva.bund.de). If this applies to you, please seek initial advice from the German Embassy or Consulate-General responsible for your place of residence. Numerous German missions abroad have information about citizenship issues on their websites.
German missions abroad: Countries A to Z