I have a question about interfaces: If an organization doesn't design or build using Object-Oriented Programming, how can internal interfaces be interpreted? As documentation of functions or procedures invoked?
Even "procedural" programs have interfaces - both intra- and inter-program interfaces.
If you're asking about internal interfaces, or intra-program interfaces, you might consider that interface descriptions and standards are a big part of this - just as much as it might be in an OOP world. These are practices that are contained with Technical Solutions, or TS, in the CMMI Model.
"C" functions have interfaces too, of course, except they're often defined by data structures that are passed, or pointers to pointers of data structures - but they're still interfaces that need to me defined and managed. Of course, OOP makes this simpler and easier to maintain, but that's another discussion!