SOP: hreflang via sitemap, done symmetrically

SOP: hreflang via sitemap, done symmetrically

Putting hreflang in the sitemap (instead of HTML head) keeps multilingual annotations in one place. The rule that breaks teams: full reciprocity.

— ✅ Every URL block lists ALL language versions including itself (xhtml:link rel="alternate")
— ✅ Annotations are reciprocal: if A points to B, B must point back to A
— ✅ One x-default per group
— ✅ Language codes are valid ISO 639-1 (+ optional ISO 3166-1 region): en, en-GB, pt-BR
— ✅ Each hreflang URL is itself canonical and returns 200

Non-reciprocal annotations are silently ignored — GSC's International Targeting / Pages report flags "no return tags".

Definition of done: for one URL group, count alternates in each member's block — all members list the identical full set.