Are you sure? I'm genuinely curious to see a reference/precedent. Also, does that restrict patentability of programming language features? (I personally can see PLs not being copyrightable, but being patentable.)
There's not really any case law I'm aware of in the US, mostly because nobody's ever tried. Copyright doesn't cover "facts, ideas, systems, or methods of operation". You can trademark the name of a language, and its documentation and any distributed software are under copyright, but the process required to translate that language into machine code isn't eligible for copyright.
Parts of the implementation might be patentable, but I don't know of any cases of anyone successfully patenting a programming language.
The Oracle vs. Google lawsuit is still going back and forth in the courts. It's worth noting that even Oracle isn't claiming that the parts of Android that involve parsing and compiling Java code are infringing on their copyright. The matter of controversy is that they claim copyright on the design of the Java standard library.
Swift's standard library is pretty much Cocoa, which isn't being rewritten here.
Are you sure? I'm genuinely curious to see a reference/precedent. Also, does that restrict patentability of programming language features? (I personally can see PLs not being copyrightable, but being patentable.)