Ok, maybe I'm missing something, I'm not C nor Objective-C dev but...

Language is just a specification, right? Which is just a document.

Then you have to implement that language using that spec: interpreter, compiler, VM, runtime, whatever.

So I was always under impression that you could implement any language in any other language (almost; sometimes with the help of another, more low-level lang, say assembly, C etc.).

It is like saying "Java has no Tail-Call optimization (yet), hence you can't implement Scheme (which requires TCO) in Java". Surely you can! Just use trampolines or even use your own stack and calling convention.

What am I missing?