GCM return null message - php

Question

I am trying to get the message from server as a push notification in android. but I got null message from server when I change language to Thai but English working.
PHP File
class GCMPushMessage {
var $url = 'https://android.googleapis.com/gcm/send';
var $serverApiKey = "";
var $devices = array();
/*
Constructor
#param $apiKeyIn the server API key
*/
function GCMPushMessage($apiKeyIn){
$this->serverApiKey = $apiKeyIn;
}
/*
Set the devices to send to
#param $deviceIds array of device tokens to send to
*/
function setDevices($deviceIds){
if(is_array($deviceIds)){
$this->devices = $deviceIds;
} else {
$this->devices = array($deviceIds);
}
}
/*
Send the message to the device
#param $message The message to send
#param $data Array of data to accompany the message
*/
function send($message, $data = false){
if(!is_array($this->devices) || count($this->devices) == 0){
$this->error("No devices set");
}
if(strlen($this->serverApiKey) < 8){
$this->error("Server API Key not set");
}
$fields = array(
'registration_ids' => $this->devices,
'data' => array( "message" => $message ),
);
if(is_array($data)){
foreach ($data as $key => $value) {
$fields['data'][$key] = $value;
}
}
$headers = array(
'Authorization: key=' . $this->serverApiKey,
'Content-Type: application/json'
);
// Open connection
$ch = curl_init();
// Set the url, number of POST vars, POST data
curl_setopt( $ch, CURLOPT_URL, $this->url );
curl_setopt( $ch, CURLOPT_POST, true );
curl_setopt( $ch, CURLOPT_HTTPHEADER, $headers);
curl_setopt( $ch, CURLOPT_RETURNTRANSFER, true );
curl_setopt( $ch, CURLOPT_POSTFIELDS, json_encode( $fields ) );
// Avoids problem with https certificate
curl_setopt( $ch, CURLOPT_SSL_VERIFYHOST, false);
curl_setopt( $ch, CURLOPT_SSL_VERIFYPEER, false);
// Execute post
$result = curl_exec($ch);
// Close connection
curl_close($ch);
echo $result;
return $result;
}
function error($msg){
echo "Android send notification failed with error:";
echo "\t" . $msg;
exit(1);
}
onMessageReceived
public void onMessageReceived(String from, Bundle data) {
String message = data.getString("message");
String title = data.getString("title");
/*Log.d(TAG, "From: " + from);
Log.d(TAG, "Message: " + message);*/
if (from.startsWith("/topics/")) {
// message received from some topic.
} else {
// normal downstream message.
}
help me please.