But who cares if there's a public body who owns the specification? The Supreme Court ruled Google's use of the copyrighted APIs fell within fair use. That gives, within the US (other countries will have other legal circumstances) a basis for anyone to copy pretty much any language so long as they steer clear of the actual copyrighted source code (don't copy MS's C# source code, for instance) and trademark violations.
I don't understand your thought process. You seem to be arguing that whether something has a proprietor is irrelevant to the question of whether it is proprietary. I cannot fathom the kind of reasoning that would lead to such a conclusion.
If the language is owned—by control and by IP—by a single corporation, it is proprietary.
Anyone can implement a compiler or interpreter for C# if they want, and there is a link to the standard for it. Is this clear enough for you?
Also, from an earlier comment you made a false claim and a strange reference.
You claimed that "most of" Java, Rust, C#, Python, and Go have only a single implementation. This is false. There are multiple implementations of each.
Second, you make a bizarre reference to "fad[ing] away like Pascal." Why do you think Pascal faded? I'll give a hint: It had nothing to do with being proprietary. At best that reference is a non sequitur, at worst it demonstrates more confusion on your part.
It isn't my reading comprehension that is deficient. You are talking in circles and demonstrating a remarkable inability to think clearly. I was just being polite.
Something being proprietary means that it is owned. It means "relating to an owner or ownership"; "of, relating to, or characteristic of an owner or title holder"; "used, made, or marketed by one having the exclusive legal right"; "privately owned and managed and run as a profit-making organization."
But who cares if there's a public body who owns the specification? The Supreme Court ruled Google's use of the copyrighted APIs fell within fair use. That gives, within the US (other countries will have other legal circumstances) a basis for anyone to copy pretty much any language so long as they steer clear of the actual copyrighted source code (don't copy MS's C# source code, for instance) and trademark violations.