Know how they got qualified to do this? By actually doing it, and by reading about others who were doing it. Modern language developers have so many shoulders of giants to sit on it's not even funny, but even so; it was only a generation ago that stuff like C didn't exist. Someone had to fill a need with a language.
Same goes for OS's/other stuff.
And sometimes, occasionally your stuff gets useful for other people -- and then they start correcting your mistakes. We are going to need one or two people who are that good at programming language design in 2039 and if it takes 24 years of putzing around and designing languages that don't work to get them there, all the power to them.