For one, a language specification is mandatory if you want to standardize it (ECMA, ISO, JIS, ...). Secondly, it paves the way for competing implementations. H

For one, a language specification is mandatory if you want to standardize it (ECMA, ISO, JIS, ...). Secondly, it paves the way for competing implementations. Having more implementations automatically means more performance, because they compete with each other. And finally, a language specification is also super useful to people who create tools such as IDEs, linters, or compilers/transpilers.