import { TranslationKey } from '../i18n/keys.js';
export type LanguageCode = string;
export declare class I18nService {
    private static instance;
    private translations;
    private currentLanguage;
    private constructor();
    static getInstance(): I18nService;
    /**
     * Asynchronously loads and sets the language for the service.
     * This is the preferred way to change languages.
     * @param lang The language code to set (e.g., 'en', 'es').
     * @returns A promise that resolves to true if the language was loaded and set, false otherwise.
     */
    setLanguage(lang: LanguageCode): Promise<boolean>;
    /**
     * Initializes the service with a default language without preloading it.
     * Call this once when your application starts.
     * @param initialLang The default language code.
     */
    init(initialLang?: LanguageCode): Promise<void>;
    getCurrentLanguage(): LanguageCode;
    /**
     * Translates a key. It's highly performant due to direct Map lookups.
     * It provides a fallback to English if a key is missing in the current language.
     * @param key The TranslationKey to translate.
     * @returns The translated string or the key itself if not found.
     */
    translate(key: TranslationKey): string;
}