If you haven’t done much other than PHP and JavaScript, I’d suggest going through the Seven Languages in Seven Weeks book, and also doing a bit of market analysis; see who’s hiring for which languages.
Personally, I can code in a few languages but I build mostly in JS. I understand why some engineers would not want to work with it and I'm not personally offended by that, but I think ES6+ can provide a great dev experience. And while there's certainly a lot of crappy jobs in the space, there also seems to be really interesting work to be found around Node / React / Vue etc.
From a freelance/consultancy niche it's almost ideal. Demand is high, and employers/clients are likely to have relatively simple requirements (i.e. a brochure/catalog site with a bit of a backend, not a huge industrial db that needs to run at planetary scale backed by a devops machine.)
It's not a personal interest but it seems to work well for people who can stand out from the pack, even a little.
My recipe for being a successful freelancer is to write clean, tested, maintainable code, PLUS specialize in some kind of niche. I mean specialize like crazy. I feel that employers like to hire polygot programmer employees because they envision them doing different things over a long period of time. But clients hire freelancers for very specific purposes and they only care about the immediate need right in front of them.
For example, my speciality is improving existing web applications written in python with Django or Flask frameworks. I can talk all day about monitoring errors in production, reducing response times, adding features, or improving app reliability, etc. But if someone asks me to support data science, build a new app from scratch, or an alexa skill, I decline.
You can definitely do well with Javascript, but again, I would be really good at one framework, such as Angular or React. Then I would focus that skill on a particular industry.