change custom data- value after ajax post success

$.post(
    url,
    {lan_setting:"en"},
    function( data, status, jqXhr ){
        alert(data.lan_setting);
    },
    "json"
);

<?php
    // do stuff

    $response = new stdClass;
    $response->lan_setting = $_POST["lan_setting"];
    print json_encode($response);
?>

/* Change few of your lines: */

<button id="loginButton" type="submit" class="btn btn-success pull-right" onclick="login(event)">Giriş</button>

AND 

function login (e) 
    {
        e.preventDefault();
        var Name = $("#userName").val();
        var Pssword = $("#userPassword").val();
        ...
        and further remains same.

// be sure to always return false, otherwise the default method would be used
function postForm(formElement) {
  if (typeof formElement === 'undefined' || !formElement) {
    // invalid call (expects at least the form element)
    return false;
  }
  // you could do some validation here, if you want, if it's unsuccesfull, show a message and return false
  // ...
  // check if the request hasn't been sent yet, if so, return false won't be resubmitted
  if (postForm.active) {
    return false;
  }
  postForm.active = true;

  // add a default option for the ajax call (in case no js is available, this option wouldn't be there
  // so you could redirect the page from aspx page)
  var data = {
      ajax: 1
    },
    hiddenElements = $('[type=hidden]'),
    i, 
      len, 
      dataKey, 
      dataValue, 
      dataItem,
      targetUrl = formElement.getAttribute('data-redirect');
  
  // get the hidden values to send that were added to the form
  for (i = 0, len = hiddenElements.length; i < len; i++) {
    dataItem = hiddenElements[i];
    dataKey = dataItem.name;
    dataValue = dataItem.value;

    if (typeof data[dataKey] !== 'undefined') {
      data[dataKey] = ',' + dataValue;
    } else {
      data[dataKey] = dataValue;
    }
  }

  // send the ajax request
  $.ajax({
    url: formElement.action,
    type: formElement.method || 'post',
    data: data,
    complete: function(response, state) {
      // free the form again (can be resubmitted at this time)
      postForm.active = false;
      if (state !== 'error') {
        // success, navigate to defined data-redirect
        window.location.assign(targetUrl);
      } else {
        // failed throw error, show message to user
        alert('Error occured during the request: ' + state);
      }
    },

  });
  // return false so that the form doesn't submit on its own
  return false;
}

// attach to all css class with name .submitter (allowing you to attach the mock submit request site wide)
$(function() {
  $('.submitter').on('click', function(e) {
    e.preventDefault();
    $('#mok').submit();
  });
});

<script src="https://ajax.googleapis.com/ajax/libs/jquery/2.1.1/jquery.min.js"></script>
<form action="[send-ajax-data-target-url]" method="post" id="mok" onsubmit="return postForm(this);" data-redirect="Confirmation.aspx">
  <input id="mail" type="hidden" value="data" name="m" />
  <button type="submit">Mock request</button>
</form>

<a href="#" class="submitter">Mock request</a>

public function test_upload()
{

    echo "<pre>";
    print_r ($_FILES);
    echo "</pre>";

}

<input type="file" name="files[]" multiple />