Unfortunately IBM Watson voices will no longer be available. We have been able to provide these voices to you for free by call IBM's cloud API via their TTS demo page. However, this goes against their terms of service, and today we can no longer do so.
IBM Watson voices use deep-learning technology to provide high quality, life-like synthetic speech. This requires a significant amount of processing power from their cloud infrastructure, and for this reason they charge a fee for the use of their TTS API. This fee is too high to be practical for Read Aloud's document-reading purposes.
If you were using these voices, please switch to different voice provider.
It would be nice if we're able to use these high-quality TTS voices for general document reading purposes. And we will be in the future, as this technology become commoditized. But in the meantime, we'll have to make do with the older generation voices that sound robotic.
Edit: for a reliable (though not very high quality) voice that works offline, please install this extension https://chrome.google.com/webstore/detail/us-english-female-text-to/pkidpnnapnfgjhfhkpmjpbckkbaodldb. After installing, the voice will appear in the voice list as "US English Female TTS (by Google)".