To use API v2 in iOS platform, we need an objective-C version

Steve,

  My wrapper is very specific to my APP.  So I do not think it would be applicable as a general API. My wrapper handles all of the errors. It's a simple object that references the Client Object and has a bunch of methods to manipulate the DB Files API. They typically return nil for error  or the primary subject of the method like the Metadata or Account info.

You mention the strong dependencies of enums for your choice of Swift. This does not really provide anything of value to the consumers of the API. It may have been useful in the implementation, You could have achieved similar results with a consistent design pattern that maps int enum value in the JSON response to an  appropriate object class. 

The types that pass across the API's  public interface  are already objects like  Metadata, Account, and Error Types..  

So you could have provided the SAME Swift User experience to users with an API written entirely in Objective-C

As I said previously: The style of passing completion blocks/closures for each request is a tremendous improvement over the previous delegate based model.