In a technical interview, what programming language (for the coding challenges) do interviewers require / want you to use?
It depends on the shop. Sometimes even pseudocode is enough.
Whatever language(s) the job your interviewing for requires. At some large companies that do entry level interviews that aren’t specific to one team/project, they will allow you to choose a language (usually C++/Java, but I think Amazon gave the option of Python as well).
Most I have participated in allow whichever language you’re most comfortable in. Usually they are generic enough algorithm/logic questions that a variety of languages can apply. If it’s a position that requires knowledge in certain languages, they might ask you do use one of those.
Thanks for all of your responses so far.