locale
Also called: language-region, locale code, language tag, bcp 47 language tag
A locale is a language plus region code (like en-US or fr-CA) that tells software which language to show and which regional conventions to use for dates, numbers, and currency. In BCP 47 form it combines a lowercase language subtag with an optional uppercase region subtag.
How a locale is built
A locale follows the BCP 47 format: a required language subtag in lowercase, an optional script subtag, then an optional region subtag written as two uppercase letters or three digits. en-US is English as written in the United States; en-GB is British English. The region part drives spelling (“color” vs “colour”), date order, number separators, and currency. So es-ES (Spain) and es-419 (Latin America) are one language but two locales your shoppers read differently.
For a store selling across markets, each locale usually needs its own crawlable URL. Google supports three patterns: a country-code domain (example.de), a subdomain (de.example.com), or a subdirectory (example.com/de/). You then tie the versions together with hreflang annotations so Google knows which URL serves which language and region.
One trap is “locale-adaptive” pages that silently swap content by the visitor’s IP or Accept-Language header. Google notes that by default Googlebot crawls from US-based IP addresses and “sends HTTP requests without setting Accept-Language,” so it may never see your other locales. Google’s own guidance is to use separate locale URLs plus hreflang rather than swapping content on a single URL.
How it affects your traffic
For a multi-market e-commerce site, locale architecture decides which country's shoppers ever find you. Miss hreflang and Google can rank your en-US page in UK results, showing dollars and US spelling to buyers who bounce. Collapse en-US, en-GB, and en-AU into one URL and you compete cleanly for none of those markets, plus you risk duplicate-content dilution. Putting each locale on its own indexable URL with correct hreflang is core e-commerce SEO work and maps directly to capturing search demand in every currency you sell in.
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