No language is a complete swiss knife, but JavaScript and Python are the closest you can go. Here I'll just point out why will you want to learn them.
I love Python, just for the readability, no other reasons required.
No language even come close to the way you can express code in python. They are highly readable and maintainable.
Python is used in multiple facets:
Pros:
Cons:
I like JavaScript because it runs everywhere.
Javascript run on almost all the devices you will see around you and that makes it an ideal candidate to learn. If you are just into web development you won't survive long without knowing JS.
Pros:
Cons:
If you asked me I will say today, surviving without javascript is difficult if not impossible. It is also very tempting to just master one language and use it everywhere. I will say learn both and use anything, what will matter is the end product or the deliverable. How fast you can solve a problem is the question? Choosing the right tool for the job is just a way to achieve it.
In the end I still love Python, but I write most of my code now a days in JS. :)