How do you write only in English language?

I have a sign up app and I want the users to write only in English!, how I can do that?

?? what exactly do you try to do that?. explain with logic blocks or some logic function...

I just don't want from the users who's going to use the app in sign up, they don't sign up using a different language like Spain or Greek, i want the text to be only in English language

you can add more allowed charactors by your self.



thank you so much I appreciate that, it worked