Является ли это то, что вы хотите?
NSDateFormatter *df = [[NSDateFormatter alloc] init];
df.calendar = [[NSCalendar alloc] initWithCalendarIdentifier:NSPersianCalendar];
df.dateStyle = NSDateFormatterMediumStyle;
df.dateFormat = @"yyyy/MM/dd";
NSString *stringDate = @"1391/04/07";
NSDate *date = [df dateFromString:stringDate];
NSLog(@"Date %@", date);
df.calendar = [NSCalendar currentCalendar]; // or this one if ur current calendar is not GregorianCalendar [[NSCalendar alloc] initWithCalendarIdentifier:NSGregorianCalendar]
NSString *stringDateConverted = [df stringFromDate:date];
[[[UIAlertView alloc] initWithTitle:nil message:stringDateConverted delegate:nil cancelButtonTitle:@"Ok" otherButtonTitles:nil] show];
Пожалуйста, проверьте Docs: https://developer.apple.com/library/mac/documentation/Cocoa/Conceptual/DatesAndTimes/Articles/dtCalendars.html –