Here is my solution that can convert Bangla number into English, and English number into Bangla.

BanglaConverter Class

<?php
class BanglaConverter {
    public static $bn = array("১", "২", "৩", "৪", "৫", "৬", "৭", "৮", "৯", "০");
    public static $en = array("1", "2", "3", "4", "5", "6", "7", "8", "9", "0");

    public static function bn2en($number) {
        return str_replace(self::$bn, self::$en, $number);
    }

    public static function en2bn($number) {
        return str_replace(self::$en, self::$bn, $number);
    }
}

echo BanglaConverter::bn2en("This is ২০১৬\n");
echo BanglaConverter::en2bn("42 আমার প্রিয় সংখ্যা\n");

Output

This is 2016
৪২ আমার প্রিয় সংখ্যা