Officially, according to the BMVI - Federal Ministry of Transport and Digital Infrastructure:
If you hold an International Driving Permit:
You must carry a translation of your domestic driving licence if
it was not issued in a Member State of the European Union (EU) or a
state party to the Agreement on the European Economic Area (EEA)
(Iceland, Liechtenstein, Norway), or
it is not in the German language, or
it does not comply with the provisions of the Convention on Road
Traffic of 8 November 1968 (Annex 6). You can find out whether your
driving licence complies with the provisions of Annex 6 by enquiring
at the appropriate authorities of the issuing state.
Annex 6 of the Convention on Road Traffic of 8 November 1968 states that each field on your driving licence needs to be numbered:
4 It is compulsory to indicate in the permit the data listed under the numbers given below:
- Family name;
- Given name, other names;
- Date and place of birth;
4.(a) Date of issue;
4.(b) Expiry date;
4.(c) Name or stamp of the authority which issued the permit;
- Number of the permit;
- Photograph of the holder;
- Signature of the holder;
- Categories (subcategories) of vehicles for which the permit is valid;
- Additional information or limitations for each category (subcategory) of vehicles in coded form.
5 If additional information is required by domestic legislation, it shall be entered on the driving permit under the numbers given below:
- (d) Identification number for the purposes of registration, other than the number under 5 of paragraph 4;
- Place of normal residence;
- Date of issue for each category (subcategory) of vehicles;
- Expiry date for each category (subcategory) of vehicles;
- Information for purposes of registration in the case of a change in country of normal residence;
- Information for purposes of registration or other information related to road traffic safety.
i.e. it should look something like this:
Notwithstanding the above, it's very likely that your driving licence would be accepted by any rental company and probably ok even if stopped by the police if your licence doesn't conform to the above. However, if it doesn't, it might be worth spending the $15 or so on an International Driving Permit.