/**
 * Lightweight wrapper around the Web Speech Synthesis API.
 *
 * This utility centralizes speaking simple, short prompts with sane defaults and
 * consistent behavior (always cancel any ongoing speech before speaking next).
 *
 * Environment
 * - Requires a browser environment with `window.speechSynthesis` support.
 * - Will throw at construction time if the API is unavailable.
 *
 * Defaults
 * - Language: auto-detected from the browser locale (configurable via constructor)
 * - Rate: 1.0, Pitch: 1.0, Volume: 1.0
 *
 * Notes
 * - The constructor primes the synthesizer by issuing an empty utterance. This
 *   can help some engines load voices before the first real `speak()` call.
 *
 * Example
 * ```ts
 * const speaker = new SpeechSynthesizer() // auto-detects language from the browser
 * speaker.speak('Stand upright')
 * // later
 * speaker.cancel() // stop any in-progress speech
 * ```
 */
export declare class SpeechSynthesizer {
    private language;
    private voice;
    private readonly isMobile;
    private readonly onVoicesChanged;
    /**
     * Create a SpeechSynthesizer with an optional preferred BCP 47 language tag.
     * If not provided, language is auto-detected from the browser locale.
     *
     * @throws Error if the Speech Synthesis API is not supported by the browser.
     */
    constructor();
    /**
     * Speak the provided text.
     *
     * Cancels any ongoing speech before speaking to avoid overlapping prompts.
     *
     * @param text - The text to synthesize.
     */
    speak(text: string): void;
    /**
     * Cancel any ongoing speech immediately.
     */
    cancel(): void;
    /**
     * Build a configured SpeechSynthesisUtterance with default parameters.
     */
    private utterance;
    /**
     * Select the best matching voice for the current language.
     */
    private selectBestVoice;
    /**
     * Map base language codes to region-specific tags for mobile voice selection.
     */
    private normalizeLanguageForMobile;
}