Language/file format for circuit-diagram description
Kind of, there is a language called VHDL-AMS and there is also spice. SPICE is good for simulation, VHDL-AMS is not widely used but is intended for hardware. Almost every software that uses a graphical approach with block diagrams or graphical symbols is a proprietary format (all of the spice packages have there own file format, all of the HDL compilers have their specific graphical format).