/**
 * Translates a given key in given language.
 *
 * @export
 * @template TSource Source of the translation set.
 * @template TLangs Available language types.
 * @param {keyof TSource} key Key of the translation set.
 * @param {TLangs} lang Language to translate.
 * @param {string} [defaultValue] Default value if the key is not found.
 * @returns The translation value or default value.
 */
export declare function _<TSource = any, TLangs extends string = string>(key: keyof TSource, lang: TLangs, defaultValue?: string): string | undefined;
/**
 * Registers a language to the translation set.
 *
 * Note that this function will check nothing if the language was existing.
 *
 * @export
 * @template TSource Source of the any language translation set.
 * @param {string} lang Language short-code to register.
 * @param {TSource} content The content of the language translation set.
 * @param {boolean} [keyCheck=false] Indicates whether the keys should be check
 * to ensure all of the mappins have the same keys.
 *
 * @returns {boolean} `true` if the language is newly registered.
 * `false` if the language was existing already and updated.
 *
 * @throws {Error} If the `keyCheck` is `true` and there are missing or more
 * keys.
 */
export declare function registerLanguage<TSource = any>(lang: string, content: TSource, keyCheck?: boolean): boolean;