Hi,
I will submit your request for a modification of this translation.
For the moment, you can override the view "frontend | your_frontend_template | checkout | term" and change the code
$text = JText::_('PLEASE_ACCEPT_TERMS_BEFORE_FINISHING_ORDER');
With
$text = JText::_('PLEASE_ACCEPT_TERMS_BEFORE_FINISHING_ORDER_MSG');
and then create a new entry in your HikaShop language override.
It will be easier for the moment to override the translation key which display in the checkout page than the error message displayed.
Regards,