A shop serves the same product page at /en-gb/kettle and /de-de/wasserkocher. How should `<link rel="alternate" hreflang="…">` be set up across those pages, and how does it interact with each page's canonical?

## What hreflang is for When the same content exists in several languages or regional variants, you do not want them treated as duplicates of one another, and you do not want a British visitor landing on the German page. `rel="alternate"` with an `hreflang` attribute annotates the set: it says "these URLs are equivalents of each other, targeted at these audiences". A search engine uses it to swap in the right version for the right user, not to change how any of them rank. ## The markup On `https://shop.example/en-gb/kettle`: ```html <link rel="alternate" hreflang="en-gb" href="https://shop.example/en-gb/kettle"> <link rel="alternate" hreflang="de-de" href="https://shop.example/de-de/wasserkocher"> <link rel="alternate" hreflang="x-default" href="https://shop.example/en-gb/kettle"> <link rel="canonical" href="https://shop.example/en-gb/kettle"> ``` On `https://shop.example/de-de/wasserkocher` the alternate block is **identical** — the same list, in the same values — and only the canonical differs, pointing at the German URL. ## The three rules that make or break it **1. Reciprocity.** Every page in the set must list every member of the set, itself included. The self-referencing alternate is the part people forget. If page A names page B but B does not name A, the annotation is treated as unconfirmed and dropped — one page's claim about another is not evidence, since anyone could point at anyone. **2. Valid codes.** The value is an ISO 639-1 language code, optionally followed by a region as an ISO 3166-1 Alpha-2 code: `de`, `de-at`, `pt-br`. Region alone is invalid — `hreflang="uk"` means Ukrainian, not the United Kingdom, and there is no way to say "United Kingdom, any language" other than by naming the language too. `x-default` is the one special value, marking the page to show when no listed audience matches. **3. Self-canonicalisation.** This is the interaction interviewers actually probe. hreflang says "these are equivalent alternatives, all of which should be indexable"; a canonical says "this one is a duplicate, index that one instead". Pointing the German page's canonical at the English URL asks the engine to drop the German page — and a page that is not indexed cannot be served as an alternate. The two annotations must agree: each localisation self-canonicalises, and the alternate set does the cross-linking. For the same reason, a page in the set must not be `noindex`. An excluded page cannot be an alternative to anything. ## Where to put the annotations Three delivery mechanisms carry the same information: - `<link>` elements in the head — the form you write by hand and the one that shows up in interviews. - Response headers, for non-HTML resources such as PDFs. - An XML sitemap, where each URL entry lists its alternates. The head form grows quadratically: with twenty locales, every one of twenty pages carries twenty links, and a single mistake breaks reciprocity for a pair. The sitemap form keeps the whole matrix in one generated file, which is why large multilingual sites usually prefer it. Whichever you choose, generate it — hand-maintained hreflang blocks drift within weeks. ## Common failures - **Missing self-reference.** The most frequent cause of a set being ignored entirely. - **Relative or non-absolute URLs**, or URLs that redirect. Point at the final, canonical URL of each localisation. - **Region-only codes** and invented values like `en-uk` (the correct code is `en-gb`). - **Alternates pointing at pages that 404, redirect, or are noindexed.** - **Language-switcher UX confused with hreflang.** The annotation helps search results; it does not automatically redirect a visitor, and auto-redirecting by IP on top of it can prevent alternates from being crawled at all. - **Assuming it affects ranking.** It affects which version is shown to whom, not how well the content ranks. ## How to check it Fetch each page's raw HTML and diff the alternate blocks — they should be identical across the set apart from the canonical. Confirm every `href` returns 200 without a redirect. If you deliver via sitemap, validate that every URL entry lists the full set. Search Console reports hreflang problems for a verified property, with "no return tag" being the standard name for a broken reciprocity pair.