Languages are API too, right? In a way. This might limit someone else's to reimplement the language's own specs? Something like LLVM will be forbidden in this

Languages are API too, right? In a way. This might limit someone else's to reimplement the language's own specs? Something like LLVM will be forbidden in this case? And Web is a complete mess, if CSS also an API? Are different JS engines will be allowed to be implemented later?