Android สอบถามเรื่องการส่งข้อมูลเข้าฐานข้อมูล MySQL ว่าทำไมพิพพ์ภาษาไทยแล้วมันไม่เป็นภาษาไทย

<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools" android:layout_width="match_parent"
    android:layout_height="match_parent" android:paddingLeft="@dimen/activity_horizontal_margin"
    android:paddingRight="@dimen/activity_horizontal_margin"
    android:paddingTop="@dimen/activity_vertical_margin"
    android:paddingBottom="@dimen/activity_vertical_margin"
    tools:context="com.example.asus.cis_project.MainActivity6"
    android:background="@drawable/logo">

    <TextView android:text="ฝากคำถาม" android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_marginTop="41dp"
        android:textStyle="bold"
        android:textSize="40dp"
        android:layout_alignParentTop="true"
        android:layout_centerHorizontal="true"
        android:id="@+id/textView196" />


    <Button
        android:layout_width="100dp"
        android:layout_height="wrap_content"
        android:text="ส่งข้อมูล"
        android:onClick="userReg"
        android:id="@+id/button"
        android:layout_alignParentBottom="true"
        android:layout_alignRight="@+id/message"
        android:layout_alignEnd="@+id/message" />

    <Button
        android:layout_width="100dp"
        android:layout_height="wrap_content"
        android:text="กลับ"
        android:id="@+id/home"
        android:layout_alignParentBottom="true" />


    <EditText
        android:layout_width="350dp"
        android:layout_height="wrap_content"
        android:hint="ชื่อ-นามสกุล"
        android:id="@+id/name"
        android:layout_below="@+id/textView196"
        android:layout_alignParentLeft="true"
        android:layout_alignParentStart="true" />

    <EditText
        android:layout_width="350dp"
        android:layout_height="wrap_content"
        android:hint="เบอร์โทร"
        android:id="@+id/tel"
        android:layout_below="@+id/name"
        android:layout_alignParentLeft="true"
        android:layout_alignParentStart="true" />

    <EditText
        android:layout_width="350dp"
        android:layout_height="wrap_content"
        android:hint="เรื่อง"
        android:id="@+id/subject"
        android:layout_below="@+id/tel"
        android:layout_alignParentLeft="true"
        android:layout_alignParentStart="true" />

    <EditText
        android:layout_width="350dp"
        android:layout_height="100dp"
        android:hint="ข้อความ"
        android:id="@+id/message"
        android:gravity="top"
        android:layout_below="@+id/subject"
        android:layout_alignParentLeft="true"
        android:layout_alignParentStart="true" />
</RelativeLayout>

import android.content.Context;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;

import android.os.AsyncTask;
import android.widget.Toast;

import com.squareup.okhttp.OkHttpClient;
import com.squareup.okhttp.Request;
import com.squareup.okhttp.Response;

import java.io.IOException;

public class BackgroundTask_2 extends AppCompatActivity {

    Context context;
    String name1, tel1, subject1, message1;

    public BackgroundTask_2(Context context,String name, String tel, String subject, String message) {
        this.context = context;
        this.name1 = name;
        this.tel1 = tel;
        this.subject1 = subject;
        this.message1 = message;
    }


    public void get_Data() {

        new AsyncTask<Void, Void, String>() {
            @Override
            protected String doInBackground(Void... voids) {
                OkHttpClient okHttpClient = new OkHttpClient();

                String name = convertToUTF8(name1);
                String tel = convertToUTF8(tel1);
                String subject = convertToUTF8(subject1);
                String message = convertToUTF8(message1);


                Request.Builder builder = new Request.Builder();
                Request request = builder.url("http://192.168.178.1/webapp/addDATA.php?user="
                        +name+"&tel="+tel+"&subject="+subject+"&message="+message).build();

                try {
                    Response response = okHttpClient.newCall(request).execute();
                    if (response.isSuccessful()) {
                        return response.body().string();
                    } else {
                        return "Not Success - code : " + response.code();
                    }
                } catch (IOException e) {
                    e.printStackTrace();
                    return "Error - " + e.getMessage();
                }
            }

            @Override
            protected void onPostExecute(String string) {
                super.onPostExecute(string);
//                Toast.makeText(getApplicationContext(), string, Toast.LENGTH_SHORT).show();
            }
        }.execute();
    }

    public static String convertToUTF8(String s) {
        String out = null;
        try {
            out = new String(s.getBytes("UTF-8"), "ISO-8859-1");
        } catch (java.io.UnsupportedEncodingException e) {
            return null;
        }
        return out;
    }



}

<?php   
 header("content-type:text/javascript;charset=utf-8");    
 $con=mysql_connect('localhost','root','1234')or die(mysql_error());    
 mysql_select_db('webappdb')or die(mysql_error());   
 mysql_query("SET NAMES UTF8");   


 $name = $_GET['user'];  
 $tel = $_GET['tel'];  
 $subject = $_GET['subject'];  
 $message = $_GET['message'];

 $sql = "INSERT INTO user (name, tel, subject, message) values('$name','$tel','$subject','$message')";  
 
 $res=mysql_query($sql);   
 $arr = array('id' => mysql_insert_id()."");  
 print('['.json_encode($arr).']');   
 mysql_close();   
 ?>

httppost.setEntity(new UrlEncodedFormEntity(nameValuePairs,"UTF-8"));

mysql_query("SET NAMES UTF8");