[pjmlp]

You should focus on algorithms and data structures.

Languages come and go, algorithms and data structures stay.

Just pick whatever language it is easier for you to learn them.

[juicy-fruit]

Of course CS fundamentals are important, I would say they build a strong foundation. However, focusing on specific technologies (mobile, CV, ML, AI, etc.) yields betters results.

[pjmlp]

Depends on the goals one wants to achieve.

In consultancy for example, what is relevant are soft skills, business domain knowledge, the technical ability to jump into whatever technology is the current hot fad and start contributing as soon as possible.