Package	`@formscript/i18n`
Specification	12, 12.2
Depends on	nothing — it is a leaf

`@formscript/i18n`

Internationalisation: the text catalogue, locale resolution and ICU message formatting, per §12 of the specification.

The catalogue

import { Catalogue } from '@formscript/i18n';

const catalogue = new Catalogue({
  'greeting': { default: 'Hello', fr: 'Bonjour' },
});

catalogue.resolve('greeting', 'fr-GB', { name: 'Ada' });

Resolution follows the fallback chain of §12.2: the exact locale, then the language, then the default. A key that resolves nowhere yields the key itself, so a missing translation is visible rather than silent.

ICU messages

The parser is a recursive descent over the ICU MessageFormat grammar, so a malformed message is reported with a position rather than throwing.

parseMessage('Hello {name}, you have {count, plural, =0 {no messages} one {# message} other {# messages}}.');

Plural rules

The plural categories follow CLDR 46, for 27 locales and 40 ordinal locales. Languages with three or six forms — Polish, Russian, Arabic, Welsh — are handled by the rules, not by a hardcoded one/other table.

The fallback is the host platform's CLDR data, never a guess.

Public API

26 exported symbols.

asDisplayString function

Brands a string as a presentation-plane value.

CatalogueEntry interface

A catalogue entry: one string, or a map of locale tag to string.

DEFAULT_LOCALE_KEY const

The reserved catalogue key holding the default-locale text (Spec-4.37).

DisplayString type

A presentation-plane value: a string at runtime, a distinct type (Spec-5.1).

formatIcuMessage function

Formats an ICU message, selecting plurals with the locale's CLDR rules.

IcuArgs interface

Named arguments supplied to a message.

IcuError class

The error raised for a malformed message.

IcuFormatOptions interface

Options that control how a message is formatted.

IcuNode type

A parsed message node.

IcuValue type

A value that can be substituted into a message.

isDisplayString function

Narrows a value to a presentation-plane string; a `display` is a string at runtime.

isSupportedPluralLocale re-export

languageOf function

The language-only form of a locale tag: `fr-CA` becomes `fr`.

Locale type

A BCP-47 language tag.

normalizeLocale function

Canonicalises a locale tag: `fr_ca` becomes `fr-CA`.

ordinalCategory re-export

parseIcuMessage function

Parses an ICU MessageFormat message into its node tree.

PLURAL_FALLBACK_LOCALE re-export

pluralCategory re-export

PluralCategory type

CLDR plural categories, in CLDR evaluation order.

pluralOperands re-export

PluralOperands interface

The CLDR plural operands derived from a number.

resolveLocaleChain function

The locale fallback chain of Spec-12.4: exact locale, language-only form, default locale.

SUPPORTED_ORDINAL_LOCALES re-export

SUPPORTED_PLURAL_LOCALES re-export

TextCatalogue class

The catalogue of user-facing text of a document.