If you are a ruby/js/go shop and you turn someone down because they only know C you are making a big mistake. If you know how to program you can learn any tech stack.
I think there are three (arguably four, depending on how you categorize) major programming paradigms. If you are competent in one, then learning other languages in the same paradigm is pretty easy because it's really just a change in syntax.
Learning a different paradigm is a bit more difficult because it requires a change in how you conceptualize the problem.