The easiest ez publish extension in the world? a filter.

extensions/<your extension>/urlfilter/lowercase.php:

<?php
 
class Lowercase 
{ 
    function process( $text, $languageObject, $caller ) 
    { 
        return strtolower($text); 
    } 
} 
?>

add the extension to your site and enable the filter in your site.ini config

[URLTranslator]
Extensions[]
Extensions[]=my_filters
Filters[]
Filters[]=Lowercase