Код добавляем в functions.php

//Rename the button on the Product page
add_filter( 'woocommerce_product_single_add_to_cart_text', 'ts_product_add_cart_button' );

function ts_product_add_cart_button( $label ) {

foreach( WC()->cart->get_cart() as $cart_item_key => $values ) {
$product = $values['data'];
if( get_the_ID() == $product->get_id() ) {
$label = __('В корзине', 'woocommerce');
}
}

return $label;

}

//Rename the button on the Shop page
add_filter( 'woocommerce_product_add_to_cart_text', 'ts_shop_add_cart_button', 99, 2 );

function ts_shop_add_cart_button( $label, $product ) {

if ( $product->get_type() == 'simple' && $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 = __('В корзине', 'woocommerce');
}
}
}
return $label;
}

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