Joomla get Language

joomGetLang.php

// get language
$lang = JFactory::getLanguage()->getLocale()[4];

if ($lang === 'en') {
    ...
}

//-----------------------------------------------------------------------------------
// inject it into javascript global namespace (e.g. in joomla template index.php)

<script>
    window.myLang = '<?php echo JFactory::getLanguage()->getLocale()[4]; ?>';
</script>