Swift : String characters (marks) are not counted correctlly

Characters as (é) or in arabic (دٌ) are counted as one in a string, how do I make it recognise the mark as a character? It should be like (د) is a character and (ٌ) is another character. I don't want to use NSString because I'm using (startIndex) which is not supported in NSString as far as I know.

Thank you