I want to get the selected language from an embedded Google translate script in a dynamic php website.

I have inserted in the head

<script type="text/javascript">
function googleTranslateElementInit() {
new google.translate.TranslateElement({pageLanguage: 'el', includedLanguages: "en,el" 
 }, 'google_translate_element');
 }
 </script>
 <script type="text/javascript" src="//translate.google.com/translate_a/element.js? 
 cb=googleTranslateElementInit"></script>

and in body:

<div style="text-align:center!important;" id="google_translate_element"></div>

and translate dropdown appears ok and does the job ok.

I want to detect the selection of the language, so I run some script depending on the selection.

So far the javascript that is executing correctly is:

<script type="text/javascript">
window.setInterval(function(){
 lang = $("select.goog-te-combo option:selected").text();
alert(lang);
 },7000);
 </script>

that shows an alert window every 7 sec with the selected language text.

How do I change the above script so that is executed only on dropdown selection change?