Change of language in PHP site according to link

I have a PHP website in three languages. I even have a changeLang (lang) function that perfectly changes the language from Portuguese to English or Spanish. However, the link on my page always stays the same, even when I change the language:

http://www.minhapagina.com/phase01?lang=pt-br

I would like the option to be able to change the language to English (eng) or Spanish (esp) when I change the link as well. I tried something like this at the top of the page phase01.php, but it did not work:

if(isset($_GET['lang'])){
    if($_GET['lang'] == 'eng'){
        echo "<script>window.addEventListener('DOMContentLoaded', function () { changeLang(1); }, false);</script>";
    }
    elseif($_GET['lang'] == 'esp'){
        echo "<script>window.addEventListener('DOMContentLoaded', function () { changeLang(2); }, false);</script>";
    }
    else {
        echo "<script>window.addEventListener('DOMContentLoaded', function () { changeLang(0); }, false);</script>";
    }
}

What could I do?