/** A locale tag (e.g. `"en"`, `"es"`, `"ja"`) — a key into a {@link Catalog}. */
export type Locale = string;
/** Flat message table for one locale: key → template string with `{param}` slots. */
export type Messages = Readonly<Record<string, string>>;
/** All locales' message tables, keyed by locale. */
export type Catalog = Readonly<Record<Locale, Messages>>;
/** Interpolation values for a message template. */
export type TParams = Readonly<Record<string, string | number>>;
/**
 * Replace `{name}` placeholders in `template` with `params[name]`. Unknown
 * placeholders are left intact. Pure and locale-independent.
 */
export declare function interpolate(template: string, params?: TParams): string;
/** Configuration for {@link createI18n}. */
export interface I18nOptions {
    catalog: Catalog;
    /** Active locale. Must be a key of `catalog` for lookups to resolve there. */
    locale: Locale;
    /** Locale consulted when a key is missing in the active locale. */
    fallbackLocale?: Locale;
    /** Invoked when a key resolves nowhere (dev warnings/telemetry); `t` still returns the key. */
    onMissing?: (key: string, locale: Locale) => void;
}
/** Runtime translator over a message {@link Catalog} — active locale, lookup with fallback, interpolation, and pluralization. */
export interface I18n {
    locale(): Locale;
    /** Switch the active locale; notifies subscribers when it actually changes. */
    setLocale(locale: Locale): void;
    /** Locales present in the catalog. */
    locales(): readonly Locale[];
    /** True when `key` resolves in the active or fallback locale. */
    has(key: string): boolean;
    /** Translate `key`, interpolating `{param}` slots; returns `key` itself if it resolves nowhere. */
    t(key: string, params?: TParams): string;
    /**
     * Plural-aware translate: picks `${key}.${category}` for the active locale's
     * Intl plural category (falling back to `${key}.other`, then `key`), with
     * `count` available as the `{count}` interpolation param.
     */
    plural(key: string, count: number, params?: TParams): string;
    subscribe(listener: () => void): () => void;
}
/**
 * Create a translator over a message catalog: active-locale lookup with a
 * fallback-locale chain, `{param}` interpolation, and `Intl.PluralRules`-based
 * pluralization. Observable (`subscribe`) so React re-renders on `setLocale`;
 * the catalog is caller-owned static data, the locale is the only state.
 *
 * @capability i18n translate a message catalog with fallback-locale lookup, `{param}` interpolation, and Intl pluralization; observable active-locale switching
 */
export declare function createI18n(options: I18nOptions): I18n;