You specify the main URL since the online search engine could possibly have problems analyzing which one particular need to be the principal URL.  The following tutorial will tell you about how to enable Canonical URLs in Prestashop one.5. PrestaShop modules we made initial to resolve the problem of https://nowbookmarks.com/story19237946/getting-my-%D0%90%D0%B2%D1%82%D0%BE%D0%BC%D0%B0%D1%82%D0%B8%D1%87%D0%B5%D1%81%D0%BA%D0%B8%D0%B5-%D1%82%D0%B5%D0%B3%D0%B8-hreflang-%D0%B8-%D0%BA%D0%B0%D0%BD%D0%BE%D0%BD%D0%B8%D1%87%D0%B5%D1%81%D0%BA%D0%B8%D0%B5-%D1%82%D0%B5%D0%B3%D0%B8-seo-to-work