First-party internationalization for JSVision applications and packages. The package provides typed catalogs, locale fallback, interpolation, cardinal plurals, selects, locale-aware formatting, catalog validation, atomic runtime overlays, and bounded diagnostics.

The default entry point is ESM-only, browser-safe, has zero runtime dependencies, and supports Node.js 22 or newer.

npm install @jsvision/i18n

Create a catalog

Catalogs use namespaced keys and canonical BCP-47 locale tags. defineCatalog validates, copies, and freezes the input before returning it.

import { defineCatalog, plural, select } from '@jsvision/i18n';

const nl = defineCatalog({
  schema: 1,
  locale: 'nl',
  messages: {
    'app.greeting': 'Hallo ${name}',
    'files.count': plural('count', {
      one: '${count} bestand',
      other: '${count} bestanden',
    }),
    'account.status': select('status', {
      active: 'Actief',
      other: 'Onbekend',
    }),
  },
});

Structured messages are intentionally shallow: each plural or select case is a string. The other case is always required. Plural selection uses Intl.PluralRules with cardinal rules for the locale of the resolved message, so applications provide the categories used by that locale rather than implementing their own singular/plural branching.

Translate and format

English is the default locale and the final implicit fallback. Later catalogs for the same locale have higher priority.

import { createI18n } from '@jsvision/i18n';

const i18n = createI18n({
  locale: 'nl-NL',
  fallbackLocales: ['de'],
  catalogs: [nl],
});

i18n.t('app.greeting', { params: { name: 'Ada' } });
i18n.t('files.count', { params: { count: 2 } });
i18n.t('dialog.cancel', { defaultMessage: 'Cancel' });

i18n.number(12345.67);
i18n.date(new Date('2026-07-25T12:00:00Z'));
i18n.compare('appel', 'peer');

Lookup tries the requested region, its base language, configured fallbacks, and finally English. If no catalog contains a key, t evaluates the English defaultMessage when supplied and otherwise returns the key. Missing translations, parameters, and controllers produce value-free diagnostics instead of interrupting rendering.

Locale auto-detection is opt-in:

const i18n = createI18n({ locale: 'auto', catalogs: [nl] });

Use an explicit locale for deterministic applications and tests.

Use one service in an application

Framework catalogs are exposed from explicit locale subpaths. Import only the requested locale, put the application catalog last, and inject the one service into createApplication:

import { datagridNl } from '@jsvision/datagrid/locales/nl';
import { filesNl } from '@jsvision/files/locales/nl';
import { formsNl } from '@jsvision/forms/locales/nl';
import { createApplication } from '@jsvision/ui';
import { uiNl } from '@jsvision/ui/locales/nl';

const i18n = createI18n({
  locale: 'nl',
  catalogs: [uiNl, formsNl, filesNl, datagridNl, applicationNl],
});

const app = createApplication({ i18n });

English remains the no-config default. The official locales are en, nl, de, fr, es, it, pt-PT, pl, ro, and sv.

Application translations and runtime overlays

Applications can layer their translations after framework catalogs. A later layer overrides only the keys it supplies:

const i18n = createI18n({
  locale: 'nl',
  catalogs: [frameworkEnglish, frameworkDutch, applicationDutch],
});

Use setCatalog to replace the highest-priority runtime overlay for one locale. Publication is atomic: an invalid replacement throws without changing the active translations.

i18n.setCatalog({
  schema: 1,
  locale: 'nl',
  messages: {
    'app.greeting': 'Welkom ${name}',
  },
});

Validate catalogs

validateCatalog returns immutable, stably ordered issues. Partial validation is suitable for application overlays. Strict validation can compare official catalogs with a reference catalog, placeholder manifest, and accelerator scopes.

import { formatCatalogIssue, validateCatalog } from '@jsvision/i18n';

const issues = validateCatalog(candidate, {
  mode: 'strict',
  referenceCatalog: english,
  placeholderManifest: {
    'files.count': ['count'],
  },
  acceleratorManifest: {
    scopes: [{ name: 'file-menu', keys: ['menu.open', 'menu.close'] }],
  },
  official: true,
});

for (const issue of issues) {
  console.error(formatCatalogIssue(issue));
}

Accelerators use JSVision's tilde markup: ~O~pen marks O, while ~~ renders one literal tilde. Strict validation requires a unique ASCII accelerator for each key listed in a scope's requiredKeys. When requiredKeys is omitted, every key in that co-visible scope is required. A translated label may remain unaccelerated by keeping it in keys for collision topology while omitting it from requiredKeys.

defineCatalog is the throwing boundary for one catalog. mergeCatalogs validates and combines ordered catalogs, with later values winning for duplicate locale/key pairs.

Diagnostics and errors

Recoverable translation faults are deduplicated and retained in i18n.diagnostics, up to 100 records. A sink can observe each new record:

const i18n = createI18n({
  diagnosticSink(diagnostic) {
    logger.warn(diagnostic);
  },
});

Diagnostics contain identities such as code, key, locale, and source; they never contain translated text or parameter values. Configuration, validation, and formatter misuse throw I18nError, which can be recognized with isI18nError.

Compatibility

ESM only.
Node.js 22 or newer.
Browser-safe default export with no node:* imports.
Zero runtime dependencies.
Uses built-in Intl implementations for locale canonicalization, formatting, collation, and cardinal plural rules.

Provenance

This JSVision-owned package adapts internationalization concepts and suitable behavioral tests from the MIT-licensed @blendsdk/i18n package. It is not a runtime dependency or a literal copy. The complete upstream attribution and license text ship with this package in THIRD_PARTY_NOTICES.md.

Migrating from BlendSDK

JSVision catalogs use { schema, locale, messages } and named message parameters. Replace BlendSDK tuple plurals with plural(parameter, cases), use select(parameter, cases) for exact variants, and pass interpolation values through t(key, { params }). File-based sources move to the explicit @jsvision/i18n/node entry point. There is no @blendsdk/i18n runtime dependency.

See the JSVision repository and documentation site for the full SDK documentation.