Is the audiobook narration better in version 1.9.24?

Yes. From version 1.9.24, pronunciation is clearer in every voice language, with the biggest improvement in Hindi, Japanese and Chinese. Spanish, French, Italian and Portuguese voices also read more cleanly. Nothing needs to be set: voice previews and new audiobooks use the improved narration after you update. An audiobook you rendered before stays as it was; render it again from the Audio page to hear the difference.