There is a known developer debug key that works in many versions of DSJ 4. This allows you to access hidden features or modify game parameters.
It's important to read this information carefully, as the game and the Polish community around it have specific terms and common pitfalls. dsj 4 1113 klucz link
Diesel Railcar Simulator relies heavily on the Steam Workshop. "Keys" in this context often refer to the requirements to unlock a specific custom scenario. There is a known developer debug key that
