PHPで月の数字を英語に変換する方法

<?php
class Num_Chinese{
    private $Month_E = array(1  => "January",
                             2  => "February",
                             3  => "March",
                             4  => "April",
                             5  => "May",
                             6  => "June",
                             7  => "July",
                             8  => "August",
                             9  => "September",
                             10 => "October",
                             11 => "November",
                             12 => "December");
    public function Month_E($Num){
        return $this -> Month_E[$Num];
    }
}
?>

<?php
require_once("./上面类函数的页面名称");
$da = new Num_Chinese();
echo $da -> Month_E(1);
?>