When you get to the point where you understand that all programming languages are just implementations of turing machines (some more limited than others), and have much experience with a few languages, I'd say yes, you can give quite good advice regardless of the language, even if you've never once used it.
If you only measure the computational power of programming languages, then it is mostly equivalent (though there are some languages which are not Turing-complete, because they have proofs of termination).
If you also measure other properties, like what kinds of guarantees your language gives you, then they differ even more.
