Suggestion

You can create an new custom field of the table "product" via the menu Display->Custom fields (in the commercial editions only) so that you can enter a page title for the product. Then, edit the file show of the view product and add the lines below just after the first <?php tag:

if(!empty($this->element->CUSTOM_FIELD_COLUMN_NAME)){
$document =& JFactory::getDocument();
$document->setTitle( $this->element->CUSTOM_FIELD_COLUMN_NAME );
}

Don't forget to replace the CUSTOM_FIELD_COLUMN_NAME by the actual column name of your custom field and the title of the product pages will be the text entered in that custom field for each products.

If you want it to be translatable via the translation file, you should use:
$document->setTitle( JText::_($this->element->CUSTOM_FIELD_COLUMN_NAME) );
instead of :
$document->setTitle( $this->element->CUSTOM_FIELD_COLUMN_NAME );
in the previous code.
Then, in your product field, you can put for example the text MY_CUSTOM_TITLE and in the translation override, you can add the line:
MY_CUSTOM_TITLE="My custom override"

Then, you need to edit the hikashop_product.xml file in the administrator/components/com_joomfish/contentelements folder, in order to add a line for your field. Then, it will be translatable via joomfish.