Sending email via mail function in base64

$messsage = base64_encode($message);
$send = mail($address, "=?utf-8?B?".base64_encode($subject)."?=", $message, "Content-type:text/plain; charset=UTF-8\r\nContent-Transfer-Encoding: base64");

How to set subject with "ru" locale in mail function (for utf-8)

$subject = "Тема сообщения";
$subject = "=?utf-8?B?".base64_encode($subject)."?=";