SF, I think it depends what your basic level is, if you can do a normal conversation I would say this is OK. Of course we use english on the flight deck, there are also some FOs who do not speak german.
ZED is a special agreement for staff travel
@EMB170 if someone flys for a company who has no agreement with other airlines he does not necessarily know what ZED is.
As far as I recall this was not a question in my ATPL exam, but maybe that has changed in the last years.
