We usually tell users to use an offline payment plugin like the bank transfer one and change the translations via an override
www.hikashop.com/en/download/languages.html#modify
At the end of the checkout, the user gets an email already with his order information.
It is trivial to add a payment link in the email via the menu System->Emails.
Just add such link:
<a href="http://mywebsite.com/index.php?option=com_hikashop&ctrl=order&task=pay&order_id=<?php echo $data->order_id; ?>">Pay now</a>
The payment on the back end though will require real coding so not so easy