import type { LocaleNameStyle } from "./getLocaleMonthNames.js";
/**
 * Return a locale's Gregorian era names as [BCE-label, CE-label].
 *
 * - The two-element array is [Before Common Era label, Common Era label].
 * - Uses the host runtime's `Intl` data via `Intl.DateTimeFormat`, so output
 *   depends on the runtime's ICU build (full-ICU runtimes localize every
 *   locale; partial-ICU runtimes fall back to English).
 * - If a locale has no distinct BCE/CE era names, both array elements
 *   contain the same string — the function never returns a sentinel for
 *   a valid locale, only for invalid input.
 * - Returns `[]` if `locale` is not a valid BCP 47 tag.
 *
 * @param locale BCP 47 locale tag (e.g. "en-US", "fr-FR", "ar-SA")
 * @param style Optional name style: `"long"` (default), `"short"`, or `"narrow"`
 * @returns 2-element `[BCE-label, CE-label]` array, or `[]` on invalid input
 *
 * @example getLocaleEraNames("en-US") // ["Before Christ", "Anno Domini"]
 * @example getLocaleEraNames("de-DE", "short") // ["v. Chr.", "n. Chr."]
 * @example getLocaleEraNames("ja-JP", "narrow") // ["BC", "AD"]
 * @example getLocaleEraNames("not-a-locale") // []
 */
export declare function getLocaleEraNames(locale: string, style?: LocaleNameStyle): string[];