Android สอบถามเรื่องการส่งข้อมูลเข้าฐานข้อมูลทำไมมันไม่เป็นภาษาไทยคับ

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;
    }



}