You specify the main URL since the online search engine could have issue identifying which a person needs to be the first URL.  The following tutorial will tell you about how to help Canonical URLs in Prestashop 1.5. The sitemap also enables you to modify any characteristics, including hreflang. https://www.presta-addons-modules.com/en/seo/prestashop-seo-automatic-google-rich-snippets-json-ld-opengraph-twitter-tags-schemaorg.html