Forbid user to use chinese in the forum

[amywangfan1985]

Hey,
I am constructing a forum right now, but I want all user to use English in my forum, and forbid people to use Chinese as their user name or post in our forum.
I added a function verify_charset(str) in install/install\vbulletin-style.xml file to check if the entered information is Chinese and changed the register form to
<form action="register.php?do=addmember" name="register" method="post" onsubmit="return verify_passwords(password, passwordconfirm)&&verify_charset(username);" class="vbform block">

But the change does not show up on the registration page. Should I reinstall it ?
Can someone please help me?

Thanks!!