Hello,
There is no usage of the translation key "RELATED_PRODUCTS" in the front-end ; only in the backend.
So I'm afraid that we don't understand what you're talking about and because you did not provide any information regarding your website, version number, link, etc ; We cannot give you any useful hint or advice.
Please clarify.
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.