Ask HN: What programming language should I learn for the web?

Mostly all of my experience is with Windows. I've configured a few Linux boxes before. I've recently started to script with PowerShell. Other than that, I've never programmed before. Also, I have a few sites running Wordpress so I've been playing with PHP.

I'm ready to dive in but there are so many choices. I don't know the pluses or minuses and I'd like to make an informed decision with an eye towards the future. I'd appreciate any help. TIA.