- str_replace: documentation ( source)
<?php
$nom = "Märie Du jean Grénaille";
$nomfilter = array(" ",'ÁÀÂÄÃÅÇÉÈÊËÍÏÎÌÑÓÒÔÖÕÚÙÛÜÝ','áàâäãåçéèêëíìîïñóòôöõúùûüýÿ');
$nomremplacement = array("_",'AAAAAACEEEEEIIIINOOOOOUUUUY','aaaaaaceeeeiiiinooooouuuuyy');
$nom = str_replace($nomfilter, $nomremplacement, $nom);
echo $nom;