In Germany there are only five circumstances in which one is allowed to change one's name:
On marriage: the couple can choose the name of one of the partners or they can keep their original names.
Correction of a name: if the state has made an error with the name and this can be proven, the original name can be restored. Example: "Maſs" became "Mahs" and is corrected to "Mass".
Unfortunate name: If a name is considered to be offensive (like "Hitler" or "Adolf", or if it is a swear word) it can be replaced by a better name.
Gender reassignment in case of transsexuals.
Naturalisation of a foreigner in Germany (Art. 47 EGBGB). In this case, the person may choose to adopt German forms of his first and last name, or a new first name if the old first name cannot be translated into German.