AJAX not passing values out to PHP

I am using Ajax to automatically update a $_SESSION value when a select option is used. Specifically, if a user selects a language from a dropdown list, $_SESSION['language'] must be update. This not happening with my implementation but I am not seeing why.

1) Select:

<select id="lang" name="lang">

                        <option value="en" data-reactid=".1.$en">English</option>

                        <option value="es" data-reactid=".1.$es">Español</option>

                        <option value="it" data-reactid=".1.$it">Italiano</option>

                        <option value="sv" data-reactid=".1.$sv">Svenska</option>

                    </select>

2) lang is passed to js and Ajax (post_language.js):

$(document).ready(function() {

$('#lang').change(function() {

    var language_selection = $(this).val();

    $.ajax({

        type: 'POST',

        url: '../includes/ajax/language_ajax.php',

        data: {lang: language_selection},

        success:function(data){

            alert('This was sent back: ' + language_selection);

            $('#lang').html(data);  

        },

        error:function(msg){

            console.log('error: '+msg);}

    });

});

});

At this point, the ALERT message appears correctly, HOWEVER, 'lang' never reaches $_SESSION echoed from within the url: language_ajax.php. In fact, the url is never even called by ajax.

3) language_ajax.php

if(isset($_POST['lang'])){



    $lang = $_POST['lang'];

    echo "Language " . $lang;

  }

I searched the forums for a few hours with no success. All solutions seem to not apply to the use of 'change' with a select list.

Can anyone help? thanks.