Adding product title(s) to new order admin email

admin_email_subject_with_product_names.php

function admin_email_subject_with_product_names( $subject, $order ) {
    $products_names = array();

    foreach ( $order->get_items() as $item ) {
        $products_names[] = $item->get_name();
    }

    return sprintf( '[%s] Nova narudžba kupca (#%s) -  %s', 
        wp_specialchars_decode(get_option('blogname'), ENT_QUOTES), 
        $order->get_id(), 
        implode(', ', $products_names)
    );
}
add_filter('woocommerce_email_subject_new_order', 'admin_email_subject_with_product_names', 10, 2);