Change add to cart text if a product is in cart on WooCommerce

In wooCommerce, I am changing add to cart button text when a product is in cart with the following code (added to functions.php of my child theme) that works well only for simple product type:

add_filter( 'woocommerce_product_single_add_to_cart_text', 'woocommerce_custom_add_cart_button_single_product' );
function woocommerce_custom_add_cart_button_single_product( $label ) {
   foreach( WC()->cart->get_cart() as $cart_item_key => $values ) {
      $product = $values['data'];
      if( get_the_ID() == $product->get_id() ) {
         $label = __('Already in Cart. Add again?', 'woocommerce');
      }
   }
   return $label;
}
// Edit Loop Pages Add to Cart
add_filter( 'woocommerce_product_add_to_cart_text', 'woocommerce_custom_add_cart_button_loop', 99, 2 );
function woocommerce_custom_add_cart_button_loop( $label, $product ) {
   if ( $product->is_purchasable() && $product->is_in_stock() ) {
      foreach( WC()->cart->get_cart() as $cart_item_key => $values ) {
         $_product = $values['data'];
         if( get_the_ID() == $_product->get_id() ) {
            $label = __('Already in Cart. Add again?', 'woocommerce');
         }
      }
   }
   return $label;
}

How to make it work for variable product type (and their product variations) too?

The following will work for simple products and variable products with product variations.

It requires jQuery to change the the add to cart button text depending on selected variation on variable products.

I have revisited your initial code completely.

// Conditional function that checks if a product is in cart and return the correct button text
function change_button_text( $product_id, $button_text ) {
    foreach( WC()->cart->get_cart() as $item ) {
        if( $product_id === $item['product_id'] ) {
            return __('Already in Cart. Add again?', 'woocommerce');
        }
    }
    return $button_text;
}

// Archive pages: For simple products (ajax add to cart button)
add_filter( 'woocommerce_product_add_to_cart_text', 'change_ajax_add_to_cart_button_text', 10, 2 );
function change_ajax_add_to_cart_button_text( $button_text, $product ) {
    if ( $product->is_type('simple') ) {
        $button_text = change_button_text( $product->get_id(), $button_text );
    }
    return $button_text;
}

// Single product pages: Simple and external products
add_filter( 'woocommerce_product_single_add_to_cart_text', 'change_single_add_to_cart_button_text', 10, 2 );
function change_single_add_to_cart_button_text( $button_text, $product ) {
    if (  ! $product->is_type('variable') ) {
        $button_text = change_button_text( $product->get_id(), $button_text );
    }
    return $button_text;
}

// Single product pages: Variable product and its variations
add_action( 'woocommerce_after_variations_form', 'action_after_variations_form_callback' );
function action_after_variations_form_callback() {
    global $product;

    // Get the produc variation Ids for the variable product
    $children_ids = $product->get_visible_children();

    $ids_in_cart  = [];

    // Loop through cart items
    foreach( WC()->cart->get_cart() as $item ) {
        if( in_array( $item['variation_id'], $children_ids ) ) {
            $ids_in_cart[] = $item['variation_id'];
        }
    }
    ?>
    <script type="text/javascript">
    jQuery(function($){
        var b = 'button.single_add_to_cart_button',
            t="<?php echo $product->single_add_to_cart_text(); ?>";

        $('form.variations_form').on('show_variation hide_variation found_variation', function(){
            $.each(<?php echo json_encode($ids_in_cart); ?>, function(j, v){
                var i = $('input[name="variation_id"]').val();
                if(v == i && i != 0 ) {
                    $(b).html('<?php _e('Already in Cart. Add again?', 'woocommerce'); ?>');
                    return false;
                } else {
                    $(b).html(t);
                }
            });
        });
    });
    </script>
    <?php
}

Code goes in functions.php file of your active child theme (or active theme). Tested and work.

On a variable product when selecting a variation:

• If the variation is not in cart (the text doesn’t change):

• If the variation is in cart (the text change):