Not if you weight by use. C, C++, Java, Javascript, and C# all have specs. Among the most popular languages, it's really only the scripting languages that have the "as our implementation does" perspective on specification. I've always used languages that have standard documents, and communities that think those standard document are very important, so rather than being unreasonable, I think of complete language documentation as the natural state of the world.
Incidentally, this isn't really a criticism, but it's precisely because I don't see Rust as finalized that it isn't. A language that's finalized but not specified is just poorly documented.
Incidentally, this isn't really a criticism, but it's precisely because I don't see Rust as finalized that it isn't. A language that's finalized but not specified is just poorly documented.