Change WooCommerce "Add to cart" text.

functions.php

<?php 

/**
* Change add to cart text in single product page
*/

add_filter('woocommerce_product_add_to_cart_text', 'modify_add_to_cart_text', 10, 2);
function modify_add_to_cart_text($product){

	global $product;
	$text = $product->is_purchasable() && $product->is_in_stock() ? __( 'My add to cart', 'textdomain' ) : __( 'Read More', 'textdomain' );
	return $text;

}

/**
* Change add to cart text in product archive
*/

add_filter('woocommerce_product_single_add_to_cart_text', 'modify_add_to_cart_text_in_single');
function modify_add_to_cart_text_in_single(){
	return __('My add to cart', 'textdomain');
}