Hreflang

Hreflang is the mechanism for telling search engines which language and region a given page targets, and which alternative versions exist for other languages or regions. It can be implemented in HTML head tags (<link rel="alternate" hreflang="...">), HTTP headers, or in XML sitemaps. All three forms are equally valid; pick one and apply it consistently.

Hreflang matters when you serve substantially the same content in multiple languages or regions and want Google to surface the right variant to each user. A US English page and a UK English page might be 95% identical content with different pricing, spelling, and contact details — hreflang lets Google pick the correct variant for searchers in each region rather than guessing.

The format uses ISO 639-1 language codes optionally combined with ISO 3166-1 Alpha 2 region codes. Examples: en (English, any region), en-US (English, United States), en-GB (English, United Kingdom), es-MX (Spanish, Mexico), x-default (the fallback for users not matching any explicit variant).

Critical rules. First, hreflang must be reciprocal — every variant in a cluster must reference every other variant, including itself. If en-US lists en-GB but en-GB does not list en-US, Google ignores the cluster. Second, hreflang must agree with Canonical Tag declarations. Each variant should self-canonical and the hreflang cluster sits on top of the canonical structure. Third, x-default is recommended for international sites with a language picker or generic fallback.

Common bugs: incomplete return tags (one-way hreflang); pointing hreflang at redirecting URLs or non-200 responses; using country codes as language codes (using "uk" for English when the correct code is "en-GB"); and canonicalising all variants to a single URL, which defeats the purpose.

For sitemap-based hreflang on large multilingual sites, group all variants of each URL in a single <url> entry with multiple xhtml:link children. This is often easier to maintain than HTML head implementation across thousands of pages.

Google Search Console's International Targeting report (now partially deprecated, but the URL Inspection tool covers similar ground) flags hreflang errors. Audit at every release that touches templates or canonicals.