Internationalisation

Pick a single URL pattern for multilingual or multi-regional content — country-code top-level domain, subdomain, or subdirectory — and stick with it. Optionally localise the slugs too.

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.

Translate every visible string in the head and in structured data — title, meta description, Open Graph fields, JSON-LD names and descriptions, image alt text — not just the body. A localised body with English metadata is a half-translation.

Declare language and regional alternates inside the XML sitemap with xhtml:link instead of in the HTML head. Easier to maintain at scale and keeps localisation metadata separate from content.

Automatically redirecting visitors to a locale based on IP geolocation or Accept-Language is an anti-pattern. It traps users in the wrong language, breaks search crawlers, and breaks shared links. Let users choose.

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.

List each locale in its own language ('Deutsch', '日本語', 'العربية') and mark it with the right lang attribute. Don't use flags — flags are countries, not languages.

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.

Vertical text (Japanese, Traditional Chinese, Mongolian) needs CSS writing-mode. Chinese, Japanese, Korean, and Thai also need explicit line-break and word-break rules so wrapping respects script-specific conventions.

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.

Most languages don't pluralise like English. Use CLDR plural categories — zero, one, two, few, many, other — via Intl.PluralRules instead of hard-coded 'item' vs 'items' logic.

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.