Hi,
Do you have any other error in your language file ?
Maybe you have another component/plugin which also create a language translation for "NEXT".
At this moment the best will be to edit the HiakShop view "front-end | your_frontend_template | checkout | step" and replace the references (two times) of
By
JText::_('HIKASHOP_CHECKOUT_NEXT')
To have a new translation key (more "unique") and add the new translation key in your override language file.
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.