An annotation identifying alternate versions of a page for different languages or regions.
Hreflang identifies alternate versions of a page intended for different languages or regions. It helps describe the relationship between those versions, such as an English product page and its French counterpart. It does not translate the content or create a localized page for you.
For Google, annotations can be supplied in HTML, HTTP headers or a sitemap. The set needs to identify the corresponding versions consistently, including the page itself. Return links matter: if one page identifies another as an alternate, the other needs to identify it in return for that relationship to be interpreted correctly.
Plan the content relationships before writing the annotations. Alternate pages should serve the corresponding audience with appropriate language and information. Do not use hreflang to label a group of unrelated service pages, or assume it is a tool for assigning individual cities within the same market. Language and supported region codes describe audiences at a different level from a list of neighborhood landing pages.
Takeaway: Use hreflang when the business genuinely maintains language or regional versions of equivalent content. Start with an accurate page-to-page mapping rather than adding codes to every URL in a template.
Example
A retailer maintains English and French versions of the same returns policy. Each version can identify the other and itself as part of the alternate set. Linking every French page to the English homepage would not describe the corresponding policies accurately, even though both destinations belong to the same business.
What to check
Check supported language and region codes, self-references and reciprocal links. A region code alone is not valid for Google’s hreflang implementation. Keep canonical choices and alternate-language relationships coherent, and do not promise that annotations guarantee a particular result for every searcher.
For more detail, see Tell Google about localized versions of your page.