I would suggest you to learn JavaScript because it is truly cross platform language. You can build web, mobile and desktop applications.

Electron:

You can build desktop application with ElectronJS. Interesting thing is you can even use almost all JavaScript libraries and frameworks with electron. Currently, I am developing a Desktop app with Electron and using VueJS for single application functionality and state management.

Ionic and React Native:

You can use either Ionic or React Native to develop mobile applications for both iOS and Android. What else you ask for? JavaScript is everywhere. As of I know, there are many companies use React for web and React Native for mobile and share 90% of same code base.

Web:

Web is overflowing with front-end JavaScript libraries and frameworks. For backend, Node.js The popular frondend libraries and frameworks are:

• jQuery,
• React
• VueJS
• Angular and
• so on.

There is no better time than now to learn JavaScript.

Kotlin might be an option, it's new and somewhat an improved java. Android adopted it. But my first answer always is: Python! Good to learn, easy to integrate, platform independent but hardly used for mobile apps (please prove me wrong as i would love to see it successfully used). Python allows for a whole slew of different programming paradigms.

Once you know programming, learning yet-another-programming-language mostly isn't that difficult (except for lisp and a few others). It's getting to know the useful libraries and tools that takes up the bulk of time.

"Not in demand" depends on what you are doing and who you are looking for work with. You go into the AAA gaming industry, OS development, API development, even language and browser development, you're not gonna find a lot of people dicking around with "tinkertoys" like PHP or node.js

But yes, if you're looking at mainstream web development and/or crapplets, then you're looking at PHP, JavaScript, and so forth.

If you're coming from C and looking for something frequently advertised or needed for lesser tasks, it would be hard to go wrong with JavaScript and/or PHP. In some ways I advise learning them in parallel, but only once you have a PROPER command of HTML and CSS.

Sad fact -- and this is more commonly a proplem with JavaScript -- is that a LOT of the people writing PHP and JavaScript right now are unqualified to do so since their main task is to either output markup or manipulate markup. PHP is best used as a 'glue' between HTML and a database, whereas client-side JavaScript should be letting the markup and style do most of the heavy lifting, only enhancing an already working page/site. If you don't know those basics, you have no business using either language for those purposes.

node.js -- basically a standalone version of Google's V8 JavaScript engine -- is a bit of a game changer there though, since it brings JavaScript to server-side development, application development, and even system services are starting to show up relying on it. Entire applications are now built with node.js sitting UNDER a browser rendering engine in addition to the scripting sitting atop it. These "full stack" web applications often being as powerful and useful as their more conventional counterparts -- just look at the Atom editor or Microsofts Visual Code Studio, both of which run on "electron", which is basically the 'blink' engine from Chrome sitting atop node.js as a runtime.

I'd bitch about the 36 megabyte runtime on desktop, but that's still smaller than a full featured JRE install!

... and whilst I favor PHP for building websites and server-side code, being able to use JavaScript in the browser, on the desktop, and on the server makes it the current go-to that just keeps growing in popularity and demand. If you don't know it already. LEARN IT!

JavaScript and Python are still going to be going strong in the future.

Lua as well, and in fact I recommend checking out Lua. It's a fun language to program in.

You can't be wrong with JavaScript. It's the language of the web.