I’m not sure that being a “better programmer” is important in web development. And I don’t mean that term in the broad sense—obviously, we should write good code—but in the sense that understanding two programming languages makes a significant difference. I think in web development it doesn’t.

Web development is about many things. HTML, CSS, performance, accessibility, security, networking, supporting different browsers, polyfills and workarounds, keeping up with new features, UX and usability. Then there are frameworks and build tools, which are all of course JavaScript-based.

Only a small part of web development is actual programming, and the fact that frameworks most of the time lay out the patterns for you, makes the “programmming” aspect even less significant in the overall picture.

So no, I don’t think that learning another programming language is a good way to spend your time if you’re a web developer.