Change the value of textfield to another language when get textfield.text in iOS

when I get mytextfield.text the result is this: "۱۲۳۴" which is a Persian number of "1234".
I have a method which converts Persian text to English text.

I want to get the English text when getting text using mytextfield.text

solution 1: I can realize when the user changes the textfield then I can change it to what I want. but its performance is not good because user might want to change it several time I just want to convert it when I want to get it.

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