I was testing out and trying to decide between the new high quality US and UK English voices. Somehow my default language for speech got locked into UK English: I can no longer change it to anything else, even though my default device language is US English and I have downloaded both the low and high quality US English voices.
See my screenshots - despite me changing my chosen language to US English in the Google Text-to-speech Engine settings in the 1st screenshot, once I hit the back button (or exit via the home / recent apps buttons), my default language reverts to UK English as per the 2nd screenshot.
Is there any system file I can edit to change this absurd behaviour? I'm rooted and willing to get my hands dirty...
I played around with settings and managed to resolve the problem.
Clearing data from / un- and re-installing the app / restoring data from another device didn't work - what did work was choosing another default device language (NOT the voice language under Text-to-speech output). This somehow released the "lock" on UK speech and allowed me to choose US instead. I then reverted the default device language to US English.
All is now good in the world