In case a Namibian certificate is to be used in Germany, it is advisable to apply for a so-called apostille (legalization of a document for international use according to the Hague Agreement from 05.10.1961, which is used in Namibia since 31.01.2001).
Apostilles are usually not issued for abridged certificates (such as abridged Birth or Marriage Certificates), therefore you have to apply for a full certificate (full Birth or Marriage Certificate) first.
The High Court of Namibia and the Ministry of Justice are able to issue an apostille.
An apostille can only be issued to an original document. It is not possible to apply for an apostille via post. It is therefore necessary to personally hand in the documents, though it is possible to send someone instead. The Embassy strongly advises against sending original documents with the post to and from Namibia. In some cases it might be necessary to have the documents pre-certified by a lawyer or a notary.
If you already in Germany, you can also commission a lawyer in Namibia to apply for an apostille on your behalf. Please contact the lawyer directly for fees and commission.