Due to circumstances beyond my control (i.e. I didn't check things carefully enough last week) the prebuilt 3.10 voice files were built with an Italian TTS voice, which obviously isn't what was intended for English text.
This error has now been corrected, and properly built voice files are now available on the download server. If you use these voice files, you might want to re-download them.
My apologies for the inconvenience