Implement hreflang for international targeting using sitemap annotations and link tags, and avoid reciprocity errors

Steps

1. Choose one of three implementation methods: HTTP Link headers, in-page link rel hreflang tags in the HTML head, or sitemap xhtml:link annotations — pick one method and apply it consistently across all versions of every page
2. For each page variant, include hreflang tags pointing to all language/region variants including the page itself; every page must self-reference its own hreflang value
3. Always include an x-default hreflang tag pointing to the fallback URL for users whose language/region does not match any defined variant
4. Validate reciprocity: every URL referenced in a hreflang annotation must itself reference back to the originating URL with a corresponding hreflang; use a crawler or a script to check cross-page consistency
5. Use BCP 47 language tags (e.g., en-US, pt-BR, zh-Hant) and verify correct region subtag casing (language lowercase, region uppercase)