i18n

Overview

Internationalisation is implemented as site-scoped language support, not a global language list. Each site declares its supported languages and primary language in packages/common/config/sites/index.ts.

That single model is reused in schema validation, editor UX, routing, and frontend data queries.

What is included

Site-specific language model

packages/common/config/sites/index.ts defines:

• primaryLanguage for fallback and default URL behaviour
• languages available for that site
• helpers such as primaryLanguageFromSite(...) and validLanguageCodeForSite(...)

This allows the same codebase to run multilingual and single-language sites together.

Schema-level language enforcement

In apps/sanity/features/translations/schema/defineLanguageField.ts, the language field:

• offers only languages valid for the current site
• validates against validLanguageCodeForSite(...)
• can be hidden/read-only once valid values are set (configurable for editorial safety)

Document types that need localisation include this field directly (for example apps/sanity/schema/types/documents/page.ts and announcements.ts).

Translation workflows in Studio

apps/sanity/sanity.config.ts wires translation tooling:

• documentInternationalization(...) for translatable document types
• internationalizedArray(...) for localised object/field values

Language is also surfaced in previews via helpers like withLanguagePreview(...), so editors can distinguish locale variants quickly.

Runtime language resolution

At request time, apps/web/src/proxy/setup-site.ts determines language by:

1. checking the first URL segment (via extractLanguageCode(...)), then
2. falling back to the site primary language (primaryLanguageFromSite(...))

Routes under apps/web/src/app/(website)/~s/[siteId]/[languageCode]/... validate site/language pairs before rendering, preventing invalid combinations.

Practical outcome

• Editors can only select valid locale values per site.
• Frontend queries remain site and language scoped.
• Default-language URLs and prefixed-language URLs are handled consistently.