How to return utf-8 when you query MYSQL

 <?php  
 header('Content-Type: application/json');  
 include 'config.php';  
  //  
 $connection = mysqli_connect($host, $user, $pass, $database) or die('ko the ke noi');  
 mysqli_query($connection, "SET NAMES 'utf8'"); // importance !  
 $sql = "SELECT * FROM `book`";  
 $result = mysqli_query($connection, $sql);  
 $json = array();  
 if ($result)  
      {  
      $row = mysqli_fetch_array($result);  
      $json["hello"] = $row['description'];  
      }  
  else  
      {  
      echo "connect success";  
      }  
 $json_print = json_encode($json, JSON_UNESCAPED_UNICODE); // print utf-8  
 echo $json_print;  
 echo $json_last_error();  
 ?>