如何解码传递给PHP的西里尔字母ajax字符串

I will ask again something similarly with risk of my question begin closed(i cannot delete the old thread,because it might get me banned,it says)..So i need to decode an ajax string which i am passing from HTML form to ajax and on to PHP.When i write in English and check values which is passed it is all right:

But when i write some in cyrillic this 'thing' is sended to php (word is "ку",same as "ku" in english)

I am trying to fix this problem from like 24 hours and read SO much information that i got overwhelmed and totally blocked. So once again there is my code:

jQuery(document).ready(function ($) {
    new InputStreamReader(conn.getInputStream(), "UTF-8")); 
    $("#food_search").keyup(function(event){
        var search_term =$(this).val();
$.ajax({
    type:"POST",
    url:"http://test.com/bg/%D1%82%D1%8A%D1%80%D1%81%D0%B5%D0%BD%D0%B5-%D0%BD%D0%B0-%D1%85%D1%80%D0%B0%D0%BD%D0%B8/",
    data:{'fsearch':search_term},
    success:function(res){
        $("#food_search_result").html(res);
        console.log(res);
    },
    error: function (xhr, ajaxOptions, thrownError) {
           alert(xhr.status);
           alert(xhr.responseText);
           alert(thrownError);
       }
});
    });
});

<script src="https://ajax.googleapis.com/ajax/libs/jquery/2.1.1/jquery.min.js"></script>
<!----------------------------------------------------------------
                              HTML
----------------------------------------------------------------->
<form method="post" accept-charset="UTF-8">
<p>Търсене на храни: <input type="text" name="fsearch" id="food_search"></p>
</form>
<div id="food_search_result"></div>
<!----------------------------------------------------------------
                              PHP
----------------------------------------------------------------->
<?php
$hostname = "localhost";
$username = "gosho";
$password = "0!ijgls9df";
$databaseName = "dbName";
$connect = new mysqli($hostname, $username, $password, $databaseName);
$fsearch="";

if(!empty($_POST['fsearch'])) {
$fsearch = $_POST['fsearch'];

$req = $connect->prepare("SELECT title FROM food_data_bg WHERE title LIKE ?");
$value = '%'.$fsearch.'%';
$req->bind_param('s', $value);
$req->execute();
$req->store_result();
$num_of_rows = $req->num_rows;
$req->bind_result($title);
if ($req->num_rows == 0){

echo 'Няма резултати';
}
else{
while($data=$req->fetch()){
   ?>
       <div class="search-result">
           <span class="result-title"><?php echo $title; ?></span>
       </div>
       <?php
       }
var_dump($_POST['fsearch']);
$req->free_result();
    }
}
?>

So for short this is Search engine which must check on every key up if there is a match in database with the inputed text and display it if there is. And my question is:

How to decode the ajax information sended to php to display cyrillic characters as usual and not like %D0%BA and so on..

If you guys need additional info,to help me feel free to ask.Thank you all <3

</div>

Guess the problem wasn't totally clear for me,but i fixed the problem the day after i asked the question.Andrew's answer is really awesome for sumbit button,but for now i won't make any button SOOO i fixed the problem by adding a single line of right AFTER the $connect and the code is:

$connect->set_charset("utf8");

The problem wasn't with any deconing,encoding atleast for now i saw that when i type like "" or / php returns \"\" or soo think for future i will need an of your advices for decoding,encoding so thank you guys ! <3 Once again i solved the problem with your help

If u wand send some data to server first of all u need serialize your data.

var request;

$("#foo").submit(function(event) {

  // Prevent default posting of form - put here to work in case of errors
  event.preventDefault();

  // Abort any pending request
  if (request) {
    request.abort();
  }
  // setup some local variables
  var $form = $(this);

  // Let's select and cache all the fields
  var $inputs = $form.find("input");

  // Serialize the data in the form
  var serializedData = $form.serialize();

  // Let's disable the inputs for the duration of the Ajax request.
  // Note: we disable elements AFTER the form data has been serialized.
  // Disabled form elements will not be serialized.
  $inputs.prop("disabled", true);

  // Fire off the request to /form.php
  request = $.ajax({
    url: "/form.php",
    type: "post",
    data: serializedData
  });

  // Callback handler that will be called on success
  request.done(function(response, textStatus, jqXHR) {
    // Log a message to the console
    console.log("Hooray, it worked!");
  });

  // Callback handler that will be called on failure
  request.fail(function(jqXHR, textStatus, errorThrown) {
    // Log the error to the console
    console.error(
      "The following error occurred: " +
      textStatus, errorThrown
    );
  });

  // Callback handler that will be called regardless
  // if the request failed or succeeded
  request.always(function() {
    // Reenable the inputs
    $inputs.prop("disabled", false);
  });

});

<form method="post" accept-charset="UTF-8" id="foo">
  <p>Търсене на храни: <input type="text" name="fsearch" id="food_search"></p>
</form>
<div id="food_search_result"></div>

PHP (that is, form.php):

$fsearch = isset($_POST['fsearch']) ? $_POST['fsearch'] : null;

And try add this code to html. documentation about this

<head>
  <meta charset="UTF-8">
</head>

</div>