<?php

function format_uri( $string, $separator = '-' )
{
    $accents_regex = '~&([a-z]{1,2})(?:acute|cedil|circ|grave|lig|orn|ring|slash|th|tilde|uml);~i';
    $special_cases = array( '&' => 'and', "'" => '');
    $string = mb_strtolower( trim( $string ), 'UTF-8' );
    $string = str_replace( array_keys($special_cases), array_values( $special_cases), $string );
    $string = preg_replace( $accents_regex, '$1', htmlentities( $string, ENT_QUOTES, 'UTF-8' ) );
    $string = preg_replace("/[^a-z0-9]/u", "$separator", $string);
    $string = preg_replace("/[$separator]+/u", "$separator", $string);
    return $string;
}

echo format_uri("#@&~^!âèêëçî");
//outputs : -and-aeeeci