The shell prompt is also a small interface. How your shell responds to tab autocomplete, provides suggestions etc. can be quite helpful. Here I just like the way fish suggests filenames, provides an underline for filenames that exist and so on.
The language is what you write in an $EDITOR. Here Elvish scripts can be nice, succinct and powerful. I like how I don't have to worry about strange "bashisms" like argument quoting etc. Everything feels consistent.
It's a shell, aren't those two things supposed to be the same basically? Or - do you mean the interaction with the terminal/command-line?