@setu-ts/localization-plugin — translate for the request locale

Add it: setu add localization adds it and prints the registration for setu.config.ts. LocalizationPlugin provides CAPABILITIES.LOCALIZATION (ILocalizer).

Configure the supported languages

Put this plugin in the config’s plugins array:

import { LocalizationPlugin } from '@setu-ts/localization-plugin';

export const localization = LocalizationPlugin({
  supportedLocales: ['en', 'de'],
  catalogues: {
    en: { greeting: 'Hello {name}', items: { one: '{count} item', other: '{count} items' } },
    de: { greeting: 'Hallo {name}', items: { one: '{count} Artikel', other: '{count} Artikel' } },
  },
});

Translate in a module route

import type { IRouterApi } from '@setu-ts/common';
import { localizerFor } from '@setu-ts/localization-plugin';

export function registerGreetingRoutes(router: IRouterApi): void {
  router.get('/greeting/:name', {
    handler: (ctx) => {
      const localizer = localizerFor(ctx);
      return ctx.response.json({ greeting: localizer.t('greeting', { name: ctx.params.name! }) });
    },
  });
}

Behaviour the types do not show

• The first supported locale is the default; every catalogue is validated during registration.
• Resolution tries the locale query, the setu_locale cookie, Accept-Language, tenantLocale, then the default. The middleware runs at priority 45, after default tenant resolution.
• Placeholders are substituted without escaping; use an escaping renderer for HTML.
• Plural messages require numeric count; a missing selected category falls back to other.
• onMissing defaults to 'key', returning the key; 'throw' raises MissingMessageError.

Other options

• Supply source instead of catalogues to load an IMessageSource once at registration.
• middleware.query: false or middleware.cookie: false disables that resolution source.
• timeZone configures formatting; allowPartialCatalogues accepts missing default-locale keys.
• exposeCatalogues: { basePath: '/i18n' } serves catalogues; replaceLocale changes a request locale.