I am not a language designer, although I've been fascinated by it for a long time. I couldn't write a compiler to save my life. But I am on the internet and do have opinions, so here is a laundry list of features my ideal language would support, or things I think might be nice to have.
0) Sane package management. What do I mean by sane package management? See how NPM does it? Not that.
1) Metaprogramming - native support for adding grammars, extending the syntax, lexing, etc. These could be distributed as packages and included as dependencies, creating a language that could be extended and improved upon by the community. The core language would probably need to allow raw memory access, pointers, and control down to assembly. In my naive fantasy, it would be possible to, say, "import javascript" then use actual javascript, possibly within a namespace or scope. Or typescript. Or lua. But probably not C++, or any language that's a Lovecraftian incantation.
2) It would support a single, possibly typed JSON-like data structure, but without required quotes for strings (so like Lua tables in that regard) but with bracket notation for arrays. Assignment in general would use the colon and not = for consistency. Or maybe it would just be s-expressions, I don't know.
2.5) Zero indexed arrays, which are the only objectively correct way to index arrays. Whitespace agnostic. If it uses semicolons and braces, they will not be optional. None of this goto fail nonsense in my language thanks.
2.6) Except goto will be supported, because a language that doesn't support unstructured control flow is a babby language.
3) Javascript-style anonymous functions and lambdas, default arguments, function overloading and multiple return values.
4) Operators as types. Any legal variable could be defined as an operator, returned from or passed to a function, etc, and could be overloaded.
I leave the implementation as an exercise for the reader.