The US Govt under Espionage and Computer Crime law (Germany ex officio), possibly breach of int treaties (FCN treaties, Germany) and ECHR for individual violations (individuals)...
There's no way a higher German court would rule against the US government on a major issue.
...possibly... but the discovery phase, witness testimony and and and ... would have more effect than a simple secrecy clause in any us court...
The US can and would just refuse to respond.
that would be telling in its own right
Would it? The broad strokes of the spying is pretty well established at this point so I'm not sure what new is actually gained in this hypothetical.