Ask HN: How to learn new technical skills as a freelancer?

I've been working with PHP, specifically Symfony (and previously Laravel) in the last years. I also do some frontend stuff (Vue.js, jQuery) and some backend and infrastructure stuff (e.g. AWS). Most of the the new stuff I learnt because I had built up some projects on my own and fortunately they are making a bit of revenue, so I can justify working on them for a few hours each week. But I'm a bit scared I'll be stuck in this role for a long time and later will be too rusty to "jump ship".

I want to learn new (technical) skills that are not currently part of my skill set. Such as Python / Flask / Django; perhaps some Node.js (since this is where the market I work in is headed) and React or even C#. Less popular languages look interesting (Haskell, Rust, etc), but as a freelancer with family including 2 small kids, I can't really find the business ROI on those languages since the freelance market is still too small.

But I am expected to jump into a project as an expert. I can do some tiny projects with new languages, but I can't bridge that part going from 'small hobby projects' to 'expert'.

Have you had successful expansions of your skill set? Or maybe transitioned into a different domain or programming language?

I've even considered becoming employed for a year or two, using a different programming language, visiting workshops, before going back to freelancing with a larger skill set.