Its important to install Silverfall first, then Silverfall: Earth Awakening. After the Download, it was mandatory to Check the files integrity, because Steam won`t install all files correctly the first time. If you installed Earth Awekening first, then Silverfall will overwrite a lot of files destroying mainly the HUD and Menue Elements.

After that, if you try to launch the Game, there will be an Error, somthing about "PhysX". You need to go into the Game files, where ypu wil find a folder with the title "PhysiX". If you have Protontricks installed, you can start the exe within that folder with Protontricks. Make sure to pick Silverfall:Earth Awakening 4470. Game will still crash on bootup trying to create D3D9 effects. Use protontricks to install d3dx9: Go to your terminal and paste this:

protontricks 4470 d3dx9

Now the game should run flawlessly.