(I don't think that the question What are the limitations of CC0 vs Public Domain investigates this issue in enough detail, so I'm asked this question to get more detail about the legal status.)
I cannot answer to the status with respect to German laws but there a few interesting precedents and commentaries that would let me think this may be a perfectly OK license for Germany (and this in contrast with a bare PD dedication which may be problematic in Germany as far as I have heard).
- The German Wikipedia uses CC0 to dedicate data into the public domain
- The Deutsche Nationalbibliothek (DNB), the German National Library, announced in 2012 they were using the CC0 for Bibliographic data.
- Dr. Till Kreutzer, a German lawyer published this paper on the CC0 where he examines if the CC0 would be valid under German laws for bibliographic metadata, likely in the context of the above or a similar one. It provides an extensive analysis. This is a dense document. Here is one of his conclusion's last statement:
Against this background the CC0 is under German law an effective means to release bibliographic metadata into the commons and to allow for their maximum usability by the general public.
In light of these and given the fact that both Wikipedia and a German Federal Agency considers it OK for them, I would think that it may be a valid license in Germany.