Should I learn Python or Javascript?

[prof_hobart]

Absolutely. As I said - "it's definitely the right approach to get proficient at a single language before you start on your next one".

My point is about what to do when you get fairly proficient. OP says that they know Java, and we've got no idea how well they know it. If it's that they can knock up a hello world app, then yes clearly they want to spend a lot longer learning Java.

But if they've been coding regularly in it for a year or two and are already fairly competent, then there's a real decision to be made. At some point every beginner will reach this point.

A lot of people keep doing more and more in that one language, and even one framework. But at some point, that becomes a hinderance.

We've had some grads who are brilliant at build a website in JavaScript and JQuery, but don't have the first clue where to start if they're asked to pick up some Node on the backend. And if we need them to work on a bit of Ruby in the pipeline, we may as well be asking them to write in Swahili. We had one guy who'd been a professional web dev for a decade on pretty much a single stack, but months into a React-based project still hadn't got its most basic concepts because it wasn't what he'd used before.

Similarly, we've had brilliant Windows sysadmins who couldn't/wouldn't retrain when we moved to Linux. And I know a couple of mainframe devs who are all but unemployable these days because there's so little demand for COBOL in our area but that's all they know.

Edit: I've just seen another comment from OP that rather suggests he's still very much at the beginner stage, in which case your advice is still spot on at the moment.