Computer science is not about learning lots of programming languages or mastering one language for the rest of your life.
It's about solving problems. One should be ready to learn whatever it takes to solve that problem. Different languages solve different problems. Some languages are created to solve particular problems, some problems can be solved by multiple languages.
Now the question is, what problem you are trying to solve? Knowing a language and not using it to solve problems is not very useful.
If you are working in front-end - Javascript
If you working in back-end - ( Javascript, Python, Java, Ruby ...... etc)
If you are working with database - ( SQL, CQL ... etc)
If you are creating something which is close to metal, need high performance - C++
If you are working on machine learning - Python, R ... etc
etc
Tip - Select a problem which interests you. Research which language solves that problem. If there are multiple languages then check out advantages and disadvantage of those languages and which on suites your problem. After that learn that language, solve that problem, if problem requires deep knowledge about that language, then master that language. It is simple, not easy.
One more thing, if you are master of X language and problem is requires Y language, your knowledge of X will be important because languages are syntactically different but conceptually most of the language are same. So concepts that you learned in X will be helpful for you to grasp Y.