To change the "includes -- VAT estimated for [country]" message on the WooCommerce checkout page, you can use the woocommerce_cart_totals_shipping_html filter.
Here's an example of how to change the message:
add_filter( 'woocommerce_cart_totals_shipping_html', 'custom_checkout_vat_message' );
function custom_checkout_vat_message( $shipping_html ) {
// Get the customer's country
$customer_country = WC()->customer->get_shipping_country();
// Get the tax rate for the customer's country
$tax_rate = WC_Tax::get_rates( $customer_country )[1]['rate'];
// Calculate the VAT amount
$vat_amount = WC()->cart->shipping_total * $tax_rate / 100;
// Format the VAT amount as a price
$formatted_vat = wc_price( $vat_amount );
// Replace the message with your custom message
$new_message = 'Price includes VAT of ' . $formatted_vat . ' for ' . $customer_country;
$shipping_html = str_replace( 'includes ' . wc_price( WC()->cart->get_shipping_tax() ) . ' VAT estimated for ' . $customer_country, $new_message, $shipping_html );
return $shipping_html;
}
In this example, we're using the WC_Tax::get_rates() method to get the tax rate for the customer's country, and then calculating the VAT amount based on the shipping total of the cart. We're then using wc_price() to format the VAT amount as a price, and replacing the original message with our custom message using str_replace().