Changing add_to_cart button text on single product pages and category view pages.

gistfile1.php

//For changing add-to-cart button text on single product pages.

add_filter('single_add_to_cart_text', 'single_cart_button_text', );

function single_cart_button_text() {
    return __('Add to order', 'woocommerce');
}

//For changing add-to-cart button text on category view pages

add_filter('add_to_cart_text', 'category_cart_button_text', );

function category_cart_button_text() {
    return __('custom text', 'woocommerce');
}