Aggiungo filtri custom post

add_action( 'restrict_manage_posts', 'filter_backend_by_taxonomies', 99, 2 );
function filter_backend_by_taxonomies( $post_type, $which ) {
if ( 'gallery' !== $post_type ) {
return;
}
$taxonomies = array( 'gallery_location', 'gallery_materials' );
foreach ( $taxonomies as $taxonomy_slug ) {
// Retrieve taxonomy data
$taxonomy_obj = get_taxonomy( $taxonomy_slug );
$taxonomy_name = $taxonomy_obj->labels->name;
// Retrieve taxonomy terms
$terms = get_terms( $taxonomy_slug );
// Display filter HTML
echo "<select name='{$taxonomy_slug}' id='{$taxonomy_slug}' class='postform'>";
echo '<option value="">' . sprintf( esc_html__( 'Show All %s', 'text_domain' ), $taxonomy_name ) . '</option>';
foreach ( $terms as $term ) {
printf(
'<option value="%1$s" %2$s>%3$s (%4$s)</option>',
$term->slug,
( ( isset( $_GET[ $taxonomy_slug ] ) && ( $_GET[ $taxonomy_slug ] == $term->slug ) ) ? ' selected="selected"' : '' ),
$term->name,
$term->count
);
}
echo '</select>';
}
}