PHP Contact form in website not sending Japanese characters - php

Question

I am using a simple php contact form that sends to an email, but when I want it to send Japanese characters, the email I receive from the form displays those characters in strange Greek-looking code. I assume there is some way to specify in the php form that I am using UTF-8, but I am not sure where or what to put to let the characters display as Japanese. Below is the code.
<?php
if(isset($_POST['email'])) {
// EDIT THE 2 LINES BELOW AS REQUIRED
$email_to = "abc#abc.com";
$email_subject = "Contact Form";
// validation expected data exists
if(!isset($_POST['first_name']) ||
!isset($_POST['email']) ||
!isset($_POST['telephone']) ||
!isset($_POST['comments'])) {
died('We are sorry, but there appears to be a problem with the form you submitted.');
}
$first_name = $_POST['first_name']; // required
$email_from = $_POST['email']; // required
$telephone = $_POST['telephone']; // not required
$comments = $_POST['comments']; // required
$email_message = "Form details below.\n\n";
function clean_string($string) {
$bad = array("content-type","bcc:","to:","cc:","href");
return str_replace($bad,"",$string);
}
$email_message .= "First Name: ".clean_string($first_name)."\n";
$email_message .= "Email: ".clean_string($email_from)."\n";
$email_message .= "Telephone: ".clean_string($telephone)."\n";
$email_message .= "Comments: ".clean_string($comments)."\n";
// create email headers
$headers = 'From: '.$email_from."\r\n".
'Reply-To: '.$email_from."\r\n" .
'X-Mailer: PHP/' . phpversion();
#mail($email_to, $email_subject, $email_message, $headers);
?>
<!-- include your own success html here -->