How to change “On Sale” text in WooCommerce

// =========================================================================
// CHANGE ON SALE TEXT
// =========================================================================
function woocommerce_custom_sale_text($text, $post, $_product){
    return '<span class="onsale">Special offer</span>';
}
add_filter('woocommerce_sale_flash', 'woocommerce_custom_sale_text', 10, 3);