50 years is a long time. If you're looking for the answer to "what should I learn now so I don't need to learn anything else in the next 50 years?" then you're approaching the whole thing in the wrong way.

There's no conflict between learning new things and "fundamentals" (however we define them). It's useful to know both. You start with the more general stuff that applies everywhere (this is a lot of what you study at university - how a computer works, how code executes, how to design a program, data structures and algorithms etc.) and then over time you pick up details like language details, specific APIs, frameworks etc.

Languages don't matter that much. Learn a few, be aware of what's out there and get comfortable with picking up new ones as you need them. It's really not a big deal.