Ask HN: What programming language should I learn when relocating to SF?

I currently live in Australia, but I'm looking to relocate to San Fran late this year.

I'm a bit of a generalist, but a developer at the core. I've been developing in PHP for years. I'm currently a Co-Founder / CTO at a 10 person company and have built several startups from the ground up, so have the whole breadth of Product Management, UX, design, marketing & ...janitorial experience that comes with that kind of role.

I'm a bit worried that most of my experience has been with PHP. I love the language, but feel like it might make it hard to me to get an exciting job in San Fran. I've still got a few months before I can move, so I'm looking for advice.

Does anyone have a suggestion or what language is best for me to spend my time learning to help when looking for a job at an early stage SF startup? Thanks!