- array_map: documentation ( source)
- var_export: documentation ( source)
- mb_strtolower: documentation ( source)
<?php
$a=['z','Z','ą', 'Ą', 'a', 'o','ó','Ó','ł','Ł','ź','A','Ż','l','ę','L','e','ć','ń','ś'];
$a=array_map($a, function($a){return mb_strtolower($a);});
$coll = new Collator( 'pl_PL' );
var_export( $a );
$coll->sort( $a );
var_export( $a );