I believe there's no past decision on this because everyone in the industry operates with the understanding that computer languages (e.g. Perl, not perl) aren't Copyrightable.
"Everyone"? Considering the kind of lawsuits and patents we have seen in the past, I don't want to put it past some companies that assume languages are copyrightable. AFAIK, it has not been tested in a *US* court (but see the remark elsewhere about a recent European decision).
I also don't think the fact that APIs aren't copyrightable is a clear cut case. After all, many APIs aren't so much designed, as that they are the outcome of the first thing the programmer wrote down (many of my APIs certainly are). As such, they would be more expressions than ideas. I don't see an API as a "fact".