i18next V4 (json)
i18next V4 is the JSON format used by the i18next internationalisation framework — one of the most widely adopted JavaScript i18n libraries. i18next is used in React applications via react-i18next, in Next.js, Node.js backends, and vanilla JavaScript projects. The V4 format extends standard JSON with specific conventions for pluralisation, namespace loading, and context keys.
i18next V4 files are valid JSON. Simple keys map to string values. Nested objects create a namespace hierarchy accessible via dot notation — auth.login.submit maps to a string inside an auth.login object. Plural forms use the underscore-suffix convention: key_one and key_other for English; key_zero, key_one, key_two, key_few, key_many, and key_other for languages with more plural categories. Interpolation uses double-brace delimited variable names. Context variants use an underscore-separated suffix.
Best practice: split translation files into namespaces — one JSON file per feature area per locale — and load namespaces lazily using the i18next backend plugin. This reduces initial bundle size and makes it easier to assign translation work to specific feature teams. Avoid dynamic key construction at runtime as this breaks the eslint-plugin-i18next static scanner. Language Monster supports i18next V4 JSON natively and preserves interpolation placeholders and plural key structure through translation.