That's cool. I had to learn some intricacies of PHP for a job once quite a while ago and the docs weren't quite sufficient. Could have used that. Language specs are typically harder to digest then other material but ultimately you can get all the details out of them you need and they're typically worth reading.
Languages that are in popular use often take decades to get there. Much of the software in the world has been there a while. The only thing surprising to me on this list is about how popular Go is after only a decade.
Also, Rust is not in the top 20? Get out of here, TIOBE index!