I agree with your idea. The main point of a motto is to reflect the philosophy and ideals that you pursue.I have some ideas, but I want to explain my chain of thoughts.
The first motto “Fast as C, Slick as Ruby” kinda explained the main points, but it was too focused on a narrow audience like Ruby developers, and that’s a problem, because from a Ruby developer’s standpoint, performance is not the first priority, as we see in the language design. Ruby developers don’t first focus on performance; they first focus on shipping features. That’s because of the language philosophy, “You write what you want to do as fast as you think, and performance issues and other stuff we will solve later”.
The second motto, “A language for humans and computers” is boring at best and confusing at worst. It doesn’t explain why developers should choose Crystal as a programming language rather than Python, Rust, Golang, Java etc., because, like, they’re also languages for humans and computers, duh.
So then, what motto to choose? My point of view is based on a quote from the Manas blog The story behind #CrystalLang | Manas.Tech
Crystal was born in June 2011 when Ary took the challenge to prove if it was possible to have a compiled Ruby-like language. The name back then was “Joy”, though three days later it was changed to Crystal. At first Crystal was just the result of the experiment.
So even the first name’s idea reflects the main philosophy: developer’s joy without performance constraints. And that’s the point; we aren’t talking about just syntax for humans, we are talking about a list of features where Crystal prevails for developers: high-level human-readable syntax with metaprogramming support, a strong static typing system, null safety by design, concurrency support, garbage collection, and fast execution speed that close to C/C++ and Rust.
So the motto must sell exactly this point. And we can even reuse the previous motto, just by adding context to the parts. In results we got something like this:
Crystal: Joyful experience for developers. Clear performance for machines.