Hi,
It seems that the issue comes from the translation of the error (which appears only above a certain amount of values in the characteristic) which has been modified on your website, and then breaking the javascript of the characteristic.
Replace the code:
alertMessage.innerHTML = '".JText::sprintf('TOO_MANY_VARIANTS',$optionsLink,$customLink)."';
to:
alertMessage.innerHTML = '".str_replace("'","\'",str_replace("\'","'",JText::sprintf('TOO_MANY_VARIANTS',$optionsLink,$customLink)))."';
in the file administrator/components/com_hikashop/views/characteristic/view.html.php and that should fix the error even without fixing the translation file.