I think the problem with this claim is that "functional programming" (or "object-oriented" "procedural") aren't actually distinguishable kinds of languages but

I think the problem with this claim is that "functional programming" (or "object-oriented" "procedural") aren't actually distinguishable kinds of languages but are more like social groups or aesthetic movements. More important question is if a language has a spec or just a default implementation, and if so if that's a compiler, interpreter, JIT etc.