Q:

Dynamically switching language PHP,Javascript, jQuery UI

I recently started implementing language options for my website.  Here is how it basically works:
if(isset($_GET['lang']))
{
    $langr= $_GET['lang'];
    $_SESSION['lang'] = $langr;
    setcookie('lang', $langr, time() + (3600 * 24 * 30));
}
elseif(isset($_SESSION['lang']))
{
    $langr = $_SESSION['lang'];
}
elseif(isset($_COOKIE['lang']))
{
    $langr = $_COOKIE['lang'];
}
else
{
    $langr = 'en';
}
switch ($langr) 
{
  case 'en':
  $lang_file = $_SERVER['DOCUMENT_ROOT']."/includes/lang/en.php";
     break;
  case 'fr':
  setlocale (LC_ALL, 'fr_FR.utf8','fra'); 
  $lang_file = $_SERVER['DOCUMENT_ROOT']."/includes/lang/fr.php";
     break;

  default:
  $lang_file = $_SERVER['DOCUMENT_ROOT']."/includes/lang/en.php";

}
include_once $lang_file;

It loads the appropriate language file at the top of every page in my website.  However, issues starting coming out when using jQuery's UI datepicker.  I found a regional settings file for the datepicker online and have created a separate file for it :
///jquery.ui.datepicker-fr.js  file

jQuery(function($){
    $.datepicker.regional['fr'] = {
        closeText: 'Fermer',
        prevText: 'Précédent',
        nextText: 'Suivant',
        currentText: 'Aujourd\'hui',
        monthNames: ['janvier', 'février', 'mars', 'avril', 'mai', 'juin',
            'juillet', 'août', 'septembre', 'octobre', 'novembre', 'décembre'],
        monthNamesShort: ['janv.', ' févr.', ' mars', 'avril', 'mai', 'juin',
            'juil.', ' août', 'sept.', ' oct.', ' nov.', ' déc.'], 
        dayNames: ['dimanche', 'lundi', 'mardi', 'mercredi', 'jeudi', 'vendredi', 'samedi'],
        dayNamesShort: ['dim.', ' lun.', ' mar.', ' mer.', ' jeu.', ' ven.', ' sam.'], 
        dayNamesMin: ['D','L','M','M','J','V','S'],
        weekHeader: 'Sem.', 
        dateFormat: 'dd/mm/yy',
        firstDay: 1,
        isRTL: false,
        showMonthAfterYear: false,
        yearSuffix: ''};
    $.datepicker.setDefaults($.datepicker.regional['fr']);
});

The issue is I need to dynamically load jquery.ui.datepicker-fr.js whenever a language change is detected so that my datepicker switches to french.  What I was thinking is creating a PHP function that I would put in my <head> that would echo out my file, but the problem with that is that not all my web pages are PHP and I don't find this a very effective method.  Any other ideas on how to do this? 

A:

You need to put a check in your header.php which will goes like that:
<script type="text/javascript>" src="/js/<?php if($_SESSION['lang'] == "en"){ echo 'datepicker-en.js'}else echo 'datepicker-fr.js'; ? >"></script>

So it will automatically detect the datepicker file according to your language parameter.