Set the document language
Set the HTML lang attribute to the language of each page, such as en or fr. This helps browsers and assistive technology interpret your content. A multilingual site still needs a language on every document.
Link equivalent translations
Add alternate hreflang links in the Astro page head for equivalent translations, including the current page. Use absolute production URLs, reciprocal links and a self-referencing canonical for each translation. x-default can identify the default language selection page. Do not link unrelated pages as translations.