How to remove the last unicode symbol from NSString

I have implemented a custom keyboard associated with a text field, so when the user presses the delete button, I remove the last character from the string, and manually update the current text field text.

NSRange range = NSMakeRange(currentTextFieldString.length-1, 1);
[currentTextFieldString replaceCharactersInRange:range withString:@""];

So far so good.

Now, the problem is, that the user has the option to enter some special unicode symbols, these are not 1 byte, they can be 2 bytes too, now on pressing the delete button, I have to remove the entire symbol, but if I follow the above approach, the user has to press the delete button twice.

Here, if I do:

NSRange range = NSMakeRange(currentTextFieldString.length-2, 2);
[currentTextFieldString replaceCharactersInRange:range withString:@""];

it works fine, but then, the normal characters, which are just 1 byte, get deleted twice at a time.

How to handle such scenarios?

Thanks in advance.

EDIT:

It is strange, that if I switch to the iPhone keyboard, it handles both cases appropriately. There must be some way to do it, there is something that I am missing, but am not able to figure out what.