i18n

Multi-language support requires separating translatable content from code, setting up locale files (JSON, YAML, or PO formats), and using libraries like i18next or react-intl to dynamically load and switch between locales. Store translations in src/locales organized by language code (e.g., en-US, fr-FR) and wire a locale selector to enable runtime switching.

Locale-aware formatting uses ICU message formats and built-in locale data to automatically adjust output based on regional conventions. Libraries like i18next and react-intl handle pluralization rules, number separators, currency symbols, and date patterns without manual string manipulation for each locale.

RTL support involves detecting the active locale and applying directional CSS or layout properties that reverse text flow and element alignment. Store RTL metadata alongside locale definitions and conditionally apply RTL classes or styling based on the selected language.

JSON, YAML, and PO/POT formats all work for storing translations. JSON and YAML integrate easily with JavaScript tooling and are simpler for small projects; PO format is standard for gettext workflows and scales well with translator tools and version control.

Fallback chains automatically load translations from a default locale (typically English) when a specific translation is unavailable. This ensures your app remains functional even with incomplete translations and reduces blank content or errors.

Yes. i18next and react-intl support multiple frameworks through dedicated integrations. For vanilla JavaScript, i18next provides a framework-agnostic core library that handles translation loading, locale switching, and formatting independently.