When people other than programmers/scientists/engineers develop programming languages, stuff like COBOL, Java and php happens, so… no thanks!
Writing your own language is surprisingly easy. It just doesn't help that much. I wrote Poslin
with a whole standard library
and I intend to continue working on both (because I actually really like it – is there any other language in which the user can add their own optimization passes? I only need to add the corresponding syntax making it easy enough…), but for the moment I do everything else in Common Lisp either way – when I need another way of expressing my idea of what the program should do, I write the macros which allow me to express it in a way that suits me.
My advice is this: Try to formulate what you want your language to be like. You can start fuzzy, but you will need to get concrete very fast.
You'll need to write prototypes to test your ideas – something that seems nice in your head might not work out when you actually try to program in it. Some stuff you thought would make your life easier might actually make programming incredibly hard because it has strange corner case behavior you didn't think of – avoiding these corner cases with checks doesn't really help, especially since it will make the semantics of your language even harder to understand.