I ended up using javascript like this inside the decision_box.inc file
<p id="customtitleplaceholder"></p>
<p id="customtextplaceholder"></p>
<script type="text/javascript">
var userLang = navigator.language || navigator.userLanguage;
switch(userLang.toLocaleLowerCase()) {
case 'en-us':
var customtitle = 'en blablabla text';
var customtext= 'fr blablablabla';
break;
case 'en-fr':
var customtitle = 'fr blablabla text';
var customtext= 'fr blablablabla';
break;
default:
var customtitle = 'en blablabla text';
var customtext = 'en blablablabla';
}
document.getElementById('customtitleplaceholder').innerHTML = customtitle
document.getElementById('customtextplaceholder').innerHTML = customtext
</script>
if you have a better way then please you're welcome to comment.