Here, the evacuation command is simple. "This is an emergency. Evacuate." (repeated in German language). While it is allowed to specify the exits to be used, doing so is left to flight crew discretion. If no exit is specified, cabin crew is to check the conditions outside on their own and decide whether using an exit is safe or not.
After an emergency landing and also a rejected takeoff, flight crew has 10 seconds to call a decision. If nothing is heard until then, cabin crew will call the flight deck and in the absence of other instructions begin to evacuate on their own account thereafter.