Hello,
The language file is where Joomla store it during the installation ; It's in the administrator part but the place is not important.
Since Joomla handle the installation, it also handle the override process.
So in your Joomla backend, under the "Extensions > Language > Overrides" you can add your overrides for these entries.
Regards,
Jerome - Obsidev.com
HikaMarket & HikaSerial developer / HikaShop core dev team.
Also helping the HikaShop support team when having some time or couldn't sleep.
By the way, do not send me private message, use the "contact us" form instead.