Berlin has alpha transparency today. Notice that everything can be seen behind a transparent window, not just the background image. Furthermore, Berlin's archicture allows for anything to be transparent, from a single widget to the entire desktop. The state of the art for graphical enviroments is pretty much pixel-based. Then the user changes the size of the fonts used for text so that he or she can read everything clearly.
Berlin supports arbitrary linear transformations of the desktop.
This means, in part, that the desktop can be scaled to any size the user wants. This makes pixel-based units more or less meaningless. Any language that has bindings for the ORB can be used to create Berlin applications. With the X Windows System, language independence usually means developing language bindings for each toolkit for each programming language. Then language bindings are further needed for the desktop API and ORB , if needed.