Hi,
With HikaSerial update and HikaShop updates, your customization is not touch.
All override files are in a external directory. This directory is safe (your template directory).
HikaShop and HikaSerial were design to be updated with customization, that's why we propose specific interfaces.
Modify core files is not recommended because your modification would be lost if you made an update, with override it's totally different.
But if you want to update manually, you have to edit the control config ( administrator/com_hikaserial/controller/config.php) and edit the 'modify' line (at the top of the file):
(code]'modify' => array('save','apply','share','send','savelanguage'),[/code]
"savelanguage" has been added in this list.
Regards,