Its fixed, Apply to transaction, not invoice.
For example :
...
$transactionPayload = new TransactionCreate();
$transactionPayload->setCurrency("EUR");
$transactionPayload->setLineItems(array($lineItem));
$transactionPayload->setAutoConfirmationEnabled(true);
$transactionPayload->setLanguage('en-US'); // set language here, pattern: 'language-COUNTRY'
$transaction = $client->getTransactionService()->create(17302, $transactionPayload);
$javaScriptUrl = $client->getTransactionIframeService()->javascriptUrl(, $transaction->getId());
...