If you think it helps to quickly write some code without types (I don't really agree with that in general, maybe in some specific cases), but you want to, when you're happy with the design, just add the types, there are many languages that support that!
On the top of my head:
* Dart (just don't give a type and the variable is dynamic)
* Groovy (add @CompileStatic or @TypeChecked when you're ready)
On the top of my head:
* Dart (just don't give a type and the variable is dynamic)
* Groovy (add @CompileStatic or @TypeChecked when you're ready)
* Racket (start using typed-racket)