When you think "language", try not to let your mind jump straight to "compiler" or "interpreter". Think more, "specification". If I asked you to write me a C compiler and you delivered on that, I'm not left with a new language. You didn't design a new language, only the compiler for an already specified language.

Designing a language is more about defining a specification. Then 10 different compiler engineers may pick that spec up and implement 10 different implementations of the same language, for example.