The most common code error: putting a country where a language belongs

The most common code error: putting a country where a language belongs

Finding from repeated audits: the highest-frequency syntactic hreflang error is a malformed value, and within that, one pattern dominates — using a country code in the language slot.

The format is language or language-REGION, where language is ISO 639-1 and region is ISO 3166-1 Alpha-2. Two failure modes:

— hreflang="en-UK" — the country code for the United Kingdom is GB, not UK. en-UK is invalid and ignored
— hreflang="uk" intending "United Kingdom" — but uk is the language code for Ukrainian. You've just told Google your UK page is in Ukrainian

Other recurring invalids: en-EU (the EU is not a country in ISO 3166-1), and language-first/region-second order reversed.

The fix: language always precedes region, and you cannot specify region alone — there is no hreflang="GB". If you want "English for Britain," it's en-gb.

A nuance that trips people: region without language is impossible, but language without region is fine and often preferable. en targets all English speakers; en-gb narrows to Britain. Don't add a region unless you genuinely differentiate by country. We'll cover that decision separately — here the point is purely: validate every code against the two ISO standards before shipping.