Ajax, PHP a čeština

    <input type="text" name="nove_jmeno_mesta" id="nove_jmeno_mesta" value="<?php echo $jmeno_mesta ?>" style="text-align: center;">
    <button onclick="nazev_zmen()">Změnit</button>
    
<script charset="windows-1250" type="text/javascript">
  
function nazev_zmen() {
    var jmeno = "<?php echo $jmeno?>";
    var nove_jmeno = document.getElementById("nove_jmeno_mesta").value;

    $.ajax({ url: '/system/jmeno_mesta_zmen.php',
        data: {jmeno: jmeno, nove_jmeno: nove_jmeno},
     type: 'POST',
     success: function() {
         location.reload();                                  
     },
       } );    
}
</script>    

<meta http-equiv="content-type" content="text/html; charset=windows-1250">
<?php
header("Content-Type: text/html; charset=windows-1250");

if(isset($_POST["jmeno"])){
    
    $dbserver         = "localhost";
    $dbusername     = "root";
    $dbpassword     = "";
    $db             = "mhra";

    $conn = new mysqli($dbserver, $dbusername, $dbpassword, $db);
    mysqli_query($conn, "SET NAMES cp1250");
    
    if ($conn->connect_error)
    {
        die("Connection failed: ".$conn->connect_error);
    }
    
    $username = $_POST['jmeno'];
    $mesto_nove_jmeno = $_POST['nove_jmeno'];
    
    $sql = "SELECT * FROM mesto WHERE hrac = '$username'";
    $result = mysqli_query($conn, $query);
    $row = mysqli_fetch_assoc($result);
    
    $jmeno_mestas = $row['jmeno_mesta'];
    
    if($jmeno_mestas == $mesto_nove_jmeno) {
        header("Location: index.php");
        die();
    } else {
        $sql = "UPDATE mesto SET jmeno_mesta = '$mesto_nove_jmeno' WHERE hrac = '$username'";
        if ($conn->query($sql) === TRUE)
        {
            header("Location: index.php");
            die();
        }
    }
    
} else {
    header("Location: index.php");
}
?>

var jmeno_n = nove_jmeno.replace(/[\u00FF-\uFFFF]/g, function(p){ return "&#" + p.charCodeAt(0) });