Your title asks about answering, but the body of your question focuses on questions, as does the scope. I think that’s important: the scope of the site is defined in terms of questions, it doesn’t limit answers.
So when answering, I would say that anything that’s helpful to answer the question is fine. I’ve written quite a few C programs to answer questions here, and in some cases I’ve even explained the process. If you have a better solution to a text-processing problem (or any other question) in Python, R, etc. than existing answers using shell or AWK, that solution certainly has its place here in my opinion.
If you want to phrase this in terms of scope compared to Stack Overflow, I’d consider things as follows:
- questions about how to write a program to do something are a better fit Stack Overflow (except when the question author specifically asks about a language which is accepted here);
- questions about how to do something on a Unix-like system are fine here.
Questions about the system’s behaviour are also fine here, and they can often involve digging into source code, often in C.
Remember that Unix’s forte (or not, depending on your point of view) has always been that it’s a self-hosted operating system designed to make it easy to develop itself, and the result is (still) that advanced system administration often ends up being programming in one way or another. In such a context, exposure to better tools and techniques is good for everyone.
(Looking at it from another angle, I often think it would be helpful to write more GUI-based answers, but it’s a lot more effort than copy-pasting commands...)