If you are referring to what Wikipedia calls eastern arabic / indic numerals, a simple replace operation should do.
$western_arabic = array('0','1','2','3','4','5','6','7','8','9');
$eastern_arabic = array('?','?','?','?','?','?','?','?','?','?');
$str = str_replace($western_arabic, $eastern_arabic, $str);
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