Hello,
Oh, I see !
Re-installing the HikaMarket package will restore the core file, including the different language files.
That's why we mostly recommend to modify the translations only if you want to share modification for the other users (thanks to the "share" button).
The HikaShop and HikaMarket language files are not updated very often, mostly when a release is made ; but because we cannot plan when the community will share translation, we do perform a mass update of them when we have enough (or if it's been too long). Since we need to check every modifications manually, it can be a complicated work.
But yes, we can see to implement the "reload" button within HikaMarket ; since all language file were already included, I didn't see the need for users.
Regards,