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

<?php 
add_filter( 'woocommerce_product_single_add_to_cart_text', 'woo_custom_cart_button_text', 999 );

function woo_custom_cart_button_text( $text ) {

	foreach( WC()->cart->get_cart() as $cart_item_key => $values ) {
		$_product = $values['data'];
	
		if( get_the_ID() == $_product->get_id() ) {
			return 'Produkt je již v košíku - přidat znovu?' ;
		}
	}
	
	return $text;
}

add_filter( 'woocommerce_product_add_to_cart_text', 'woo_archive_custom_cart_button_text', 999 );

function woo_archive_custom_cart_button_text( $text ) {

	foreach( WC()->cart->get_cart() as $cart_item_key => $values ) {
		$_product = $values['data'];
	
		if( get_the_ID() == $_product->get_id() ) {
			return 'Produkt je v košíku';
		}
	}
	
	return $text;
}