If you want to nitpick, Germany technically doesn't have copyright in the US sense and instead the term is usually considered equivalent to what is called Urheberrecht (author's rights), which is indeed not transferrable.

You can however grant an unlimited, transferrable, exclusive license, which for all intents and purposes is like "transferring copyright".

Your nitpick isn't entirely irrelevant though. This is why Germany does not recognize public domain dedications and why CC0 is necessary.

I think that in civil law countries you can sometimes give / sell away your copy rights, but never your moral rights ?

(Though copy rights themselves might also be treated as actual rights, rather than a temporary monopoly, an exception to the normal state of everything being in the public domain that prevails in the common law countries ?)