Hi,
In each product, you have a field "canonical URL". If you've filled this field AND you have the "force canonical URL on listing" setting activated in the HikaShop configuration, then you will be redirected to that link when you are on the listing and click to access the product page.
So if you have a website in several languages, either you leave that field empty so that HiksShop generates the link to the product page for each language, or your need to enter the canonical URL for each translation of the product (in the popup which opens when you click on the flags of the product edition page) so that the system can redirect to the canonical URL of the current language.
If you only enter the canonical URL in the product and not in the translations, then regardless of the language you use to display the listing, it will always use that canonical URL and it will be the same for all the languages and thus you see that "language switch" you're talking about.