Update localized strings

Refactor of the API error description static strings because localized strings defined like so:
```
NSString * const foo = @"foo";
NSString *localizedFoo = NSLocalizedString(foo, nil);
```
are not picked up by the genstrings tool.

Generating strings: http://www.delitestudio.com/app/localizable-strings-merge/
The default genstrings tool does not recursively search .m files or handle merges well