One trend I've noted in coding interviews (Go look on YouTube for "Interviewing.io technical interview") is that most of them involve asking the interviewee to code some algorithm by hand. By hand meaning that languages such as Java and Python often provide algorithms but the interviewee is asked to not use those and instead to write their own.
This is what C pretty much always does since it does not have many built-in data structures. So I wanted to highlight that C is a great language to learn for practicing writing your own hashtables, maps, and string functions. It can be a bit daunting when trying to code practical high level apps in C but for interview practice, it's really a great language because it has no training wheels and forces you to think algorithmically.