How do we solve an AXSpeechAssetDownloader error on iOS?
I was having the same issue. I couldn't find any help, so, I had to debug it by trying various things.
What I found is that if you access Settings -> General -> Speech, and enable "Speak Selection" and muck about with the English voice, it will just start working for you.
Let me know if this helps.
This means that the resources required to speak the required languages have not been downloaded, and the app failed to do that automatically. as @softwarenerd mentions, you can go to Settings -> General -> Speech, and then go to Voices and download whatever voices you need.
But then, this is not really a good solution if you are developing the app for the app store. There must be a way to handle the download automatically and on demand.