It depends on what I'm doing but usually Go if an application requires any longevity at all.

I use Python or Java for things that require more dynamic typing. The main usecase here is big data or to prototype applications.

Bash I usually reserve for very small tasks. When I bootstrap services in containers, you'll usually find some Bash. A whole CLI written in Bash? I would not approve that PR. Bash lacks variable scoping for the most part, the ways in which you can implement it are hacky and non-obvious. Bash's syntax and the way it behaves varies by system, even installer scripts have to account for this. As I'm typing this, I realize the Bash code I write generally follows the same testing and constraints as the Makefiles I write.

I don't think I really understand the requirement for "a single document". This departs from programming practices I've built up over the years. When I come across large multi-thousand LOC documents (in any language, much less Bash) I'm usually concerned.