change-add-to-cart-button-text.php

<?php

/**
 * Change "Add to cart" button text
 */
add_filter( 'woocommerce_product_single_add_to_cart_text', 'ywp_override_add_to_cart_text', PHP_MAX_INT );
add_filter( 'woocommerce_product_add_to_cart_text', 'ywp_override_add_to_cart_text', PHP_MAX_INT );  
function ywp_override_add_to_cart_text() {
    return 'ثبت سفارش'; 
}

// The code goes to your active theme (or child theme) functions.php