am {TranslationsParent} [translationsParent]
   */
  startTranslation(languagePair, port, translationsParent) {
    const innerWindowId = translationsParent?.innerWindowId;
    if (translationsParent) {
      this.#translationsParents.set(innerWindowId, translationsParent);
    }
    if (this.#isDestroyed) {
      throw new Error("The translation engine process was already destroyed.");
    }
    const transferables = [port];
    this.sendAsyncMessage(
      "TranslationsEngine:StartTranslation",
      {
        languagePair,
        innerWindowId,
        port,
      },
      transferables
    );
  }

  /**
   * Remove all the translations that are currently queued, and remove
   * the communication port.
   *
   * @param {number} innerWindowId
   */
  discardTranslations(innerWindowId) {
    this.#translationsParents.delete(innerWindowId);
    if (this.#isDestroyed) {
      return;
    }

    this.sendAsyncMessage("TranslationsEngine:DiscardTranslations", {
      innerWindowId,
    });
  }

  /**
   * Manually shut down the engines, typically for testing purposes.
   */
  forceShutdown() {
    return this.sendQuery("TranslationsEngine:ForceShutdown");
  }

  #isDestroyed = false;

  didDestroy() {
    this.#isDestroyed = true;
  }
}
PK