Programming is a lot like Linux. It is a lot less scary once you actually get into it. That being said, what is the ONE language you should learn? The one that will determine your career? Simple. C++. I am not joking, here's why.

C++ is an extension to C. If it makes it easier, think of it like TypeScript and JavaScript, but lower level with different syntax. Why C++ in particular? First, it can run plain C code in any sane C++ compiler. Second, you can learn everything lower level and can aim higher level if you so wish.

But I am an x developer, and C++ doesn't fit my work: Other than web development, this isn't an issue but let's say it is. You still have one core thing to do, learn the absolute core. If you focus on Web-Dev (somewhere where C++ actually doesn't make sense), then learn the core of programming by doing C++ part-time.

But C++ is complicated: That's why I choose C++. As if you want to learn how Linux works, use Arch, not Ubuntu. If you just need to get a job done and you don't want to learn too much, then learn Python. Python is a wonderful language for those who don't care to actually program (just get things working). This isn't an insult to Python, by the way, it is the selling point of why even I use it even though it isn't my favorite. But C++'s complexity can prepare you for jumping languages as you wish.

But y language seems more my taste: Cool, learn C++ anyways. At the VERY least, just look into how it works and what everything is. How I wrote Fibonacci in 35 languages (before it became a team project with 60 languages, 2 others that weren't to the cut we required) is that I learned from doing... originally JavaScript... and applied what I knew in JavaScript and looked how the things were done in that language.

But I like other styles like LISP and Java: C++ is still valuable. It teaches you the core of programming, and LISP and Java styles don't add too much else than a syntax overhaul. You will be doing the same things in C++ than in Java.

I am a functional programmer: ... Yeah then don't learn C++. C++ is an OOP and while it can still be applied, Haskell and Elixir are far leaps from C++. Unless it is a mixed language like F# where it can be functional and OOP.

Okay, where do I go learn C++: YouTube has many good tutorials. I recommend C++ Tutorial 2020 by Derek Banas and C++ Tutorial for Beginners from Giraffe Acadamy (uploaded by freeCodeCamp) at least to start. Then feel free to go elsewhere and learn a tutorial by whomever.