非英语语言问题来自数据库

我想将数据从PHP发送到Android手机 . 对于API调用，我正在使用“REST”

在我的PHP中，我的所有角色都是非英语语言（泰米尔语） . 所以我使用utf-8在数据库中插入非英语（泰米尔语）内容 .

所有字符都插入到DB中，我将数据作为json发送到Android . 但是我在Android开发方面的问题，虽然获取json文件，但他们获得的所有字符都像问号（???????） .

我是这个领域的新手，我不知道如何解决这个错误 .

这是我使用的PHP脚本：

<?php 
    require_once 'DbConnect.php';

    mysql_query('SET character_set_results=utf8');
    mysql_query('SET names=utf8');
    mysql_query('SET character_set_client=utf8');
    mysql_query('SET character_set_connection=utf8');
    mysql_query('SET collation_connection=utf8_general_ci');    

    $response = array();


    if(isset($_GET['apicall'])){

        switch($_GET['apicall']){


            case 'question':

                // i am get lesson and chapter name as request from application side ,i will match lesson and chapter and send question 
                $lesson  = $_POST['lesson'];
                $chapter = $_POST['chapter'];

                if(!isset($lesson) || !isset($chapter)){
                    $response['error'] = true; 
                $response['message'] = 'key and values is empty (or) wrong';
                http_response_code(404); 
                    }



                if(isTheseParametersAvailable(array('lesson','chapter'))){
                    //getting values 
                 $lesson = $_POST['lesson'];
                 $chapter = $_POST['chapter']; 

                    //creating the query 


                 $result1 = mysqli_query($conn, $query1);

                  $query = "SELECT que_desc,true_ans FROM question WHERE lesson = '".$lesson."' AND chapter = '".$chapter."' ";

                    $result = mysqli_query($conn, $query);
                   // $user =array();
                    $i=1;

                    while($row = mysqli_fetch_assoc($result))
                    {
                        $question = $row['que_desc'];
                        $true_ans = $row['true_ans'];
                        $response['question'][$i] = $question;
                        $response['ans'][$i] = $true_ans;

                        $i++;

                    }


                         mysqli_set_charset($link, 'utf8');


                         header('Content-Type: application/json');
                        echo json_encode($response , JSON_FORCE_OBJECT);
                        exit;


                }
            break; 



                default: 
                $response['error'] = true; 
                $response['message'] = 'Invalid Operation Called';
                http_response_code(404);

            }

    }else{
        //if it is not api call 
        //pushing appropriate values to response array 
        $response['error'] = true; 
        $response['message'] = 'Invalid API Call';
            http_response_code(404);
    }

    //displaying the response in json structure 
    header('Content-Type: application/json');
    echo json_encode($response);

    //function validating all the paramters are available
    //we will pass the required parameters to this function 
    function isTheseParametersAvailable($params){

        //traversing through all the parameters 
        foreach($params as $param){
            //if the paramter is not available
            if(!isset($_POST[$param])){
                //return false 
                return false; 
            }
        }
        //return true if every param is available 
        return true; 
    }

    if($_SERVER['REQUEST_METHOD'] ==  "GET"){
        $response['method_type'] = "wrong";
        $response['status'] = 0;
        http_response_code(404);

    header('Content-Type: application/json');
    echo json_encode($response);

    }


    ?>

This is my DB response on Android side任何人请帮我解决这个错误 . 提前致谢