At the very least he should not ask which language, but should be able to be to analyze what are the pro's and con's of a language and take six weeks each to be able to be proficient in them.
He is a computer science student, you wrote. A language is just a tool, does he understand that? Theory is way more important.
Computer languages are not rocket science, the theory behind them makes rocket science implementable, not possible.
Most CS people have way more than an understanding of just one computer language because they are not restricted to that: get the theory right and you should be able to learn any computer language. (If it is Turing complete...)
It may very well be that if his Master focusses on math, he will choose Fortran, or if his subject is string oriented, he would choose Pascal, of if he is in a rush chooses Python or if he want to shoot himself in the foot choose C.
Note these are all languages from my past: I have just (two years ago) started to pick up Haskell.
Get the point?
A CS student should be able to have sufficient knowledge to make the choice for the right tool, even better: he should me able to make the right tool for what he needs.
Compiler engineering is craft, not science. Computer science is.