Hi,
The translation key HIKA_VARIANTS_MIDDLE_SEPARATOR is for the separator between each characteristic value.
By default this is a space and you can change it with a translation override.
The translation key HIKA_VARIANT_SEPARATOR is for the separator between the product name and the characteristics values.
By default this is a : and you can change it with a translation override.
In both cases, this can be done by editing your translation file via the Languages tab of the HikaShop configuration page and adding the translation key in the "override" area at the bottom of the popup, as explained in here:
hikashop.com/download/languages.html#modify
So, for HIKA_VARIANTS_MIDDLE_SEPARATOR, you would add such line if you want the values on different lines:
HIKA_VARIANTS_MIDDLE_SEPARATOR="<br/>"
And for HIKA_VARIANT_SEPARATOR, you would add such line if you don't want the : character after the product name:
HIKA_VARIANT_SEPARATOR=" "