Relevant for what? The question isn't really complete.<p>Is PHP still a language in use, should I support it if I build tools or platforms for programmers? Sure. It's in use in many places.<p>Is PHP still a language worth learning if I intend to do agency style web development? Probably yeah. It still has a high showing in that domain.<p>Is PHP relevant for someone writing brand new distributed systems? Probably not. It has poor ergonomics and a bad concurrency story, and there are better languages for any criteria you care about.<p>Is PHP relevant outside of backend web services? No, and it never has been.<p>Is PHP relevant for PL research? Absolutely not. PHP's language design is almost wholly parasitic. It has few ideas of its own.<p>But... that's not really what we're writing about, when we're writing about relevance. Relevance here is a value judgement. But it's not PHP's quality as a language that makes it so ubiquitous. PHP is largely widespread because for a long time it had by far and away the best deployment story. You could get a LAMP server provisioned and be up within minutes.<p>I think the really interesting question is, "based on what made PHP so ubiquitous, what's the next PHP?". And I think the answer is JavaScript.<p>JS is quickly becoming the platform of least resistance. I can write a script and have it served on AWS Lambda within seconds. I can go into my function code and add logging on the fly. I have the same fast feedback cycle, in other words, that I would have had with PHP fifteen years ago.<p>I'm becoming more and more convinced that the most powerful tool a language can provide is a REPL. The faster I can turn abstract ideas concrete, the better. And the next generation of programming languages will live or die on their "playability".