hydrocontrol:
It could be a problem with the settings of the TTS app. What kind of settings does it have?
baud rate?
serial port?
I think this is a blind alley. These adjustments are not available at the Android end. If Bluetooth is working, it's working. No grey areas. As I said before, this can be proven with a standard Bluetooth terminal.
The last card in the pack at the Arduino end may be the formatting of the text, whereby anything will work on a terminal but the TTS is more particular. If this is the case, there should be a note to that effect with the TTS app.
Failing that, the last par in reply #23 is a really good idea.