Implementing a Custom Shell

So, if I were trying to write my own implementation of a fully bash-compatible UNIX shell, what standards and/or functionalities should I be aware of, and where would I look for the best information?

Also, would there be any perceived downside to using a language other than C? Perhaps Go or Rust?
I have no problem with C. In fact, I'm most familiar with it. But I'm curious about the implications of the use of other languages in building such system utilities, and how it might affect development as well as the end-user's experience.