I am having problems understanding your questions. I generally operate on level 2 and we typically use graphics based languages when we implement scripting languages to do graphical languages. The two most common graphic languages are FBDs and Ladder-Logic. Both have a general form and vendor specific quirks.

For scripting I tend towards Perl or Python, but I have seen other guys use different methods.

Level 3 use pretty much the same tools. Level 4 I have in the passed used a modbus/tcp method but this isn’t something I can really say is typical. One guy I know used the python API to do it.