Internationalisation

hreflang tells search engines which language or regional version of a page to show to which user. It uses BCP 47 codes and must be reciprocal across all alternates.

Mark passages, phrases, and inline elements that differ from the document language with a lang attribute. WCAG 3.1.2 requires it so assistive tech can switch pronunciation.

Sites that serve Arabic, Hebrew, Persian, or Urdu must set dir="rtl" and use CSS logical properties so layouts mirror correctly without hard-coded left and right.

Dates, numbers, currency, and units should be formatted in the user's locale. Use Intl APIs in the browser and the same locale data server-side so output matches expectations.

IDNs let domain names contain non-ASCII characters. They are encoded as Punycode on the wire and rendered as Unicode in the browser, subject to anti-spoofing rules.