I think those symbols are just learned.

Take folders. They look like this: http://upload.wikimedia.org/wikipedia/en/5/50/Earthwise.jpg

That makes it obvious where the symbol is coming from. The only problem is that those kinds of folders are not commonly used in Germany. I think I never saw a folder like that before I started using computers.

Folders look like this in Germany: http://upload.wikimedia.org/wikipedia/commons/d/d9/Lever_arc...

The word that is used in Germany to refer to folders („Ordner“ in German) actually refers to ring binders.

Yet I had never a problem dealing with folders on computers, even though the visual metaphor was unfamiliar to me.