- 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;