Ah understand now -
will have to check with the boss but I don't think there is anything coded for this.
What I just tried and works fine is to use lang vars in the display template and use Joomla language over-rides
so in file templates/YOUR_TEMPLATE/html/com_virtuemart/productdetails/default.php around line 921 change to
<?php if (!empty($customTab1_title)) {?>
<div id="customTab2" class="tabcontent" style="display:none;">
<?php echo JText::_('PUREMART_SHIP_TAB');
#echo $params->get('productdetails_customTab1_content');; ?>
</div>
<?php } ?>
you can also use this technique in the tab titles - around line 823
<?php $customTab1_title = $params->get('productdetails_customTab1_title');
if (!empty($customTab1_title)) {?>
<li><a href="javascript:void(0)" rel="#customTab1">
<span>
<?php
echo JText::_('PUREMART_SHIP_TAB_TITLE');
#echo $customTab1_title;
?>
</span></a></li>
<?php } ?>
As I say - I will check with the boss but this does work fine
Cheers