Speaking of implicit dependencies, here are a few: env, path, any executable file either in the current directory or in the search path. env = functions and aliases, and can be modified by any shell script. The path is an implicit dependency in the sense any chmod +x files in any of these directories can affect the shell. Which means the shell is also dependent on the file system itself.

True enough, though as soon as you have dependencies, you can't guarantee cross-platform or cross-version portability with those other languages either.