Glossary
hreflang
hreflang is an HTML attribute and HTTP header that tells search engines which language and regional version of a page to serve to a given user. Essential for international SEO.
hreflang is used on multilingual or multi-regional sites to indicate equivalent versions of a page in different languages or regions. Example: a SaaS company with /en, /de, and /fr versions of their pricing page uses hreflang to tell Google 'these three pages mean the same thing, in different languages — show the right one to the right user.'
Implementation: a `<link rel='alternate' hreflang='LANG-COUNTRY' href='URL'>` tag in the `<head>` of EVERY language version, pointing to all the OTHER language versions AND back to the current page itself (self-reference is required). Same can be done via HTTP `Link` header or in the XML sitemap.
hreflang values: language code (`en`, `de`, `fr`), language + country (`en-US`, `en-GB`, `de-DE`, `pt-BR`), or `x-default` for the fallback version shown when no language matches. Use language-only when targeting any speaker of the language; use language + country when distinguishing British English from American English, or Brazilian Portuguese from European Portuguese.
Common hreflang mistakes: missing the self-reference (a /en page that doesn't include `hreflang='en'` pointing to itself is invalid); inconsistent reciprocal links (page A links to page B, but page B doesn't link back to page A); using country codes when there's no real regional distinction (`en-US` and `en-GB` are usually wrong unless content actually differs); pointing hreflang at pages that redirect (must be canonical URLs).
When to skip hreflang: monolingual sites, or multilingual sites with very different content per locale (in which case the pages aren't equivalents and shouldn't be cross-linked via hreflang). Use canonical tags instead when pages target the same query in the same language but with minor variations.
Example
A SaaS launches /en, /de, /es, /pt-br, /ja versions of its pricing page. Each page includes 5 hreflang tags pointing to all the others plus itself plus `x-default` pointing at the English version. Google starts serving the Japanese version to Japanese-IP queries within 14 days; organic traffic from Japan grows 6× over 3 months.