It's not a real law but there are certain guidelines that are followed. A name can be rejected by the authorities in which case the child's parents can file a claim.
The guidelines are the following:
- it can't be a brand or company name (p.ex. Coca
Cola)
- it can't be harmful to the child because of bad associations (p.ex.
Adolf)
- it can't be a last name or a title
- it has to respect the religious feelings of others (that's why Christus isn't allowed)
German written law only states that everybody has to have at least one first name and it has to be registered until one month after birth at latest.
I hope this was interesting to you.