That's not my experience with Julia. I find it easy to add type annotations where you want - but it's not needed that often. Usually I add it for clarity, not for performance reasons, like I would in Python.

And I definitely don't get what you mean by having to write the code twice: To me the beauty of Julia is exactly that you write it once, then optimise it for speed (or robustness, with gradual typing and all) instead of rewriting it in another language.

Unfortunately, I also don't agree that the runtime error messages are good in Julia. I find them pretty bad :( even if stack traces are good. And also, the lack of automatic type checking in the editor is also a problem for productivity.