Hreflang is an HTML attribute (or equivalent XML sitemap or HTTP header annotation) that signals to search engines which language and region a page targets.
Hreflang is emitted as <link rel="alternate" hreflang="..." href="..."> in the document head, listing every locale variant of the page. Each variant in the cluster must reciprocate — link A to B requires link B back to A — or Google ignores the entire cluster. A special value x-default designates the fallback variant when no specific language matches.
Hreflang does not directly affect rankings. Its purpose is selection: Google uses hreflang to choose which locale variant to display to which user. Correct hreflang prevents the English variant from outranking the German variant in Germany, which translates to measurable conversion lift in regional markets.
AI engines (Perplexity, ChatGPT, Claude) have weaker hreflang awareness than Google. Best practice in 2026 is to combine hreflang with locale-specific Markdown twins and explicit inLanguage properties in JSON-LD.