Actually, D is a real thing: https://en.wikipedia.org/wiki/D_(programming_language)
And so is E: https://en.wikipedia.org/wiki/E_(programming_language)
And F (though it can be argued that it's a subset of Fortran): https://en.wikipedia.org/wiki/F_(programming_language)
So, if you're making a new language that's supposed to replace C, call it G. The letters even look kind of similar.
Microsoft has a programming language called P