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.

The translate attribute marks content that automatic translation systems must leave alone - brand names, code, and identifiers. Use translate="no" so Google Translate and the browser's built-in translation don't mangle terms that have no localised form.

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.