Text-based languages can still be very different from one another. There's only the appearance of similarity now because most programming languages, and all mainstream ones, are descendants of ALGOL60, influenced to a greater or lesser extent by Smalltalk and Lisp. There's almost nothing in common between Prolog and C, for example.
How can you read any program without the (source) code on hand? The same problem occurs, for example, with Java byte code.
And programming as a directed graph isn't a bad idea, but there must be a canonical, easily readable, textual format, that is the DEFAULT, regardless of how you manipulate it.