Xavier, thank you very much for the prompt reply. I spent the time since your reply repeatedly trying to do this and I am failing.
I did precisely what you said to do. I actually made the following change not only in the order.php, but in the overrides too, to make sure I was calling the right code:
if(empty($order->mail->subject)) {
$order->mail->subject = JText::sprintf('NEW_ORDER_SUBJECT',$order->order_number,HIKASHOP_LIVE,$order->customer->name);
I found that I had to DELETE the usual subject line in the email template, but I cut and pasted your language modifications precisely as you indicate. And then on the tests, I get:
New order No. D7C1 created on http://[site url]/, cust name:
The constant is there, but the variable data for the name is just not being called properly.
Is there anything else I can try? THANKS.