Glossary

hreflang

An HTML and sitemap signal that tells search engines which URL serves which language/region — Google's primary mechanism for ranking the right page per audience.

hreflang annotations tell Google (and Yandex) which URL on your site corresponds to which language/region. Without them, Google may serve your English page to a French searcher, halving CTR.

Declare them in three places (Google reads any of them):

<link rel="alternate" hreflang="…" href="…"> in <head>
<xhtml:link> per entry in your XML sitemap
HTTP Link headers

Always include hreflang="x-default" pointing at the locale shown when no other rule matches.