Javascript comes to mind, since it only functionally has I think 5 types (string, number, boolean, array, object - and the line between array and object is blur

Javascript comes to mind, since it only functionally has I think 5 types (string, number, boolean, array, object - and the line between array and object is blurry) and no user-added ones. There are no built-in type semantics whatsoever other than what properties are present on an object at the time of its use. Functions of different arities aren't even type-differentiable (although arity is available as a reflectable value).