You specify the key URL because the search engine can have difficulty pinpointing which just one needs to be the main URL.  The subsequent tutorial will tell you about how you can enable Canonical URLs in Prestashop 1.5. You will find 3 ways to include hreflang tags to webpages https://addons.prestashop.com/fr/seo-referencement-naturel/31857-seo-automatique-google-rich-snippets-json-ld-open-graph.html