How to change server side language cookies like client side using Ajax?

I have two news websites, one in Spanish and one in English:

es.example.com // Spanish
example.com // English

But from the main domain (in English) I am integrating a system to be able to show news in another language for example:

example.com/es/url-de-la-noticia/ // Spanish

Based on that URL, I create one ´cookie´ where the language of the URL will be stored, which is the first folder/subfolder or directory ´/es/´:

//I create the cookies automatically for the subdomain and for the URLs in Spanish.
if($FOLDER_LANG === "es" || $SUBDOMAIN_LANG === "es") {
    setcookie ('language', 'es', time()+60*60*24*365, '/', '.example.com');
}

With this parameter, news will be displayed in Spanish for both the site: es.example.com by the subdomain es or by the URLs in Spanish example.com/es/url-de-la-noticia/ = es

//We verify the existence of the cookie
if(isset($_COOKIE['language'])){
    //We print variables of the language in coincidence of the value that the cookie stores
    if($_COOKIE['language']==='en'){
        $website_title = " | Sitio en español";
        $lang = 'es';
        $language = "es";
    }elseif($_COOKIE['language']==='es'){
        $website_title = " | WebSite Ingles";
        $lang = 'en';
        $language = "en";
    }
} else {
    //In case there is no cookie, I show the English language by default.
    $website_title = " | WebSite Ingles";
    $lang = 'en';
    $language = "en";
}

So far everything seems to be working properly.

But the problem arises when I try to change the language through Ajax, although the Ajax code does send and send information, for some reason it does not replace the cookie, that is, if I click on the English language, it does not change it, the change of language.

What I want to achieve is that the language can also be changed, removing or replacing the cookies both on the server side and the client side using ajax:

$(function(){
    var tnum = 'en';
    
    $(document).click( function(e) {
        $('.language, .more_lang').removeClass('active');
    });

    $('.language .current_lang').click(function(e){
        e.stopPropagation();
        $(this).parent().toggleClass('active');
        setTimeout(function(){
            $('.more_lang').toggleClass('active');
        }, 5);
    });

    $('.more_lang .lang').click(function(){
        $(this).addClass('selected').siblings().removeClass('selected');
        $('.more_lang').removeClass('active');

        var img = $(this).find('img').attr('src');
        var lang = $(this).attr('data-value');
        var tnum = lang;

        $('.current_lang .lang-txt').text(lang);
        $('.current_lang img').attr('src', img);

        //if(lang == 'ar'){}
    });
});

$(function() {
    $(".lang").click(function(e) {
        e.preventDefault();
        var language = $(this).attr('data-value');
        var postData={lang: language};

        var request = $.ajax({
            method : 'POST',
            url    : 'language.ini.php',
            data   : postData,
            dataType: "html"
        });
        request.done(function(data) {
            $(".resultado").html(data);
        });
        request.fail(function(jqXHR, textStatus) {
            alert("Ocurrió un error: " + textStatus);
        });
    });
});

body{
    margin:0;
  padding:0;
  color:#444444;
  font-family: 'News Cycle', sans-serif;
}

.language{
  position:fixed;
  z-index:1;
  top:20px;
  left:20px;
  font-size:16px;
  background:#fff;  
  border-radius:4px;
}

.current_lang{
  cursor:pointer;
  text-transform:uppercase;
  overflow:hidden;
}

.lang{
    padding:10px 15px;
}

.lang.selected{
  display:none;
}

.lang img, 
.lang span.lang-txt{
  display:inline-block;
  margin-left:5px;
  vertical-align:middle;
}

.lang span.lang-txt{
   position:relative;
  top:-1px;
  font-weight:700;
}

.lang img{
  width:20px;
  margin-left:0;
}

.lang span span{
  color:#999;
  font-weight:400;
}

.lang span.fa{
  font-size:12px;
  position:relative;
  top:-1px;
  margin-left:3px;
}


/*more lang*/
.more_lang{
  transform:translateY(-20px);
  opacity:0;
  cursor:pointer;
  display:none;
   -webkit-transition: all .3s cubic-bezier(.25, 1.15, .35, 1.15);
    -moz-transition:    all .3s cubic-bezier(.25, 1.15, .35, 1.15);
    -o-transition:      all .3s cubic-bezier(.25, 1.15, .35, 1.15);
    -ms-transition:     all .3s cubic-bezier(.25, 1.15, .35, 1.15);
    transition:         all .3s cubic-bezier(.25, 1.15, .35, 1.15);
}

.language.active .more_lang{
  display:block; 
}

.more_lang.active{
  opacity:1;
   transform:translateY(-0px);
}

.more_lang .lang:hover{
  background:#5766b2;
  color:#fff;
}

.more_lang .lang:hover span{
  color:#fff;
}

.language:hover,
.language.active,
.content a:hover{
  box-shadow:rgba(0,0,0,0.2) 0 5px 15px;  
  -webkit-transition: all 0.3s cubic-bezier(0,.99,.44,.99);
    -moz-transition:    all 0.3s cubic-bezier(0,.99,.44,.99);
    -o-transition:      all 0.3s cubic-bezier(0,.99,.44,.99);
    -ms-transition:     all 0.3s cubic-bezier(0,.99,.44,.99);
    transition:         all 0.3s cubic-bezier(0,.99,.44,.99);
  
}

.language.active .lang{
  border-bottom:1px solid #eaeaea;
}

/*CONTENT*/
.content{
  width:100%;
  max-width:400px;
  position:absolute;
  top:50%;
  left:50%;
  -ms-transform: translateX(-50%) translateY(-50%);
  -webkit-transform: translate(-50%,-50%);
  transform: translate(-50%,-50%);
  border-radius:2px;
  padding:20px;
  -webkit-box-sizing: border-box;
    -moz-box-sizing: border-box;
    box-sizing: border-box;
  
  text-align:center;
}

.content h1, 
.content h2, 
.content p{
  margin:0;
}

.content p{
   line-height:22px;
  text-align:left;
  margin-top:15px;
}


.content div.ct-img{
  width:150px;
  height:150px;
  overflow:hidden;
  border-radius:50%;
  margin:0 auto 10px;
}

.content div img{
  height:100%;
  position:relative;
  left:-30px;
}

.content a{
  padding: 8px 15px 10px;
   border-radius:4px;
  background:#5766b2;
  color:#fff;
  text-decoration:none;
  display:inline-block;
  margin-top:25px;
  position:relative;
  overflow:hidden;
}

.content a:active{
  transform: scale(0.9);
   -webkit-transform: scale(0.9);
  -moz-transform: scale(0.9);
}

/*RTL*/
body[dir="rtl"] .language{
  right:20px;
  left:auto;
}

body[dir="rtl"] .lang span.fa{
  margin-right:3px;
  margin-left:0;
}

body[dir="rtl"] .lang .lang-txt{
  margin-right:5px;
  margin-left:0;
}

body[dir="rtl"] .content div img{
  left:auto;
  right:-30px;
}


body[dir="rtl"] .content p{
  text-align:right;
}

body[dir="rtl"] .lang span span{
  float:left;
  margin-right:5px;
}

<script src="https://cdnjs.cloudflare.com/ajax/libs/jquery/3.3.1/jquery.min.js"></script>
<div class="language">
        <div class="current_lang">
            <div class="lang" data-value='en'>
                <img src="https://image.flaticon.com/icons/svg/299/299722.svg">
                <span class="lang-txt">EN</span> 
                <span class="fa fa-chevron-down chevron"></span>
            </div>
        </div>
        <div class="more_lang">    
            <div class="lang selected" data-value='en'>
                <img src="https://image.flaticon.com/icons/svg/299/299722.svg">
                <span class="lang-txt">English<span> (US)</span></span>
            </div>
            <div class="lang" data-value='es'>
                <img src="https://image.flaticon.com/icons/svg/299/299820.svg">
                <span class="lang-txt">Español</span>
            </div>
        </div>
    </div>

The language.ini.php file will be in charge of changing the language, creating their respective cookies.

<?php
    if (isset($_POST['lang'])) {
        $lang = $_POST['lang'] ?: '';
    
        if ($lang === "en") {
            setcookie ('language', 'en', time()+60*60*24*365, '/', 'example.com');
        } elseif ($lang === "es") {
            setcookie ('language', 'es', time()+60*60*24*365, '/', 'es.example.com');
        }
    }
?>

from How to change server side language cookies like client side using Ajax?