How to stop Ubuntu from talking to me?

Pressing AltSuperS will disable or enable speech dispatcher.

The last thing you should hear is "screen reader off" :-

ps. The Super key is the "windows" key...

Go to the Settings application. Select Universal Access. You will see a tab labeled "Seeing". In there should be Screen Reader. Turn that off.

I had the same problem maybe, starting with Ubuntu 15.04. The Screen reader is off, same with the dispatcher setting; but it keeps telling me what I'm typing.

I have running four dispatcher, all at the time that can't be killed because they're starting again directly. To solve my problem, I went to System Settings -> Sound. On Applications, I muted the four speech-dispatcher.

Do you want to change the systemwide settings for Speech Dispatcher? The (yes/no) systemwide settings for Speech Dispatcher can be changed by editing the /etc/default/speech-dispatcher file.

Open the terminal and from the terminal open the /etc/default/speech-dispatcher file for editing in nano text editor:

sudo nano '/etc/default/speech-dispatcher'  

Find the lines in speech-dispatcher that say:

# Set to yes to start system wide Speech Dispatcher
RUN=yes

...and change RUN=yes to RUN=no.

This will disable the system wide speech dispatcher audible notifications, if they have been previously enabled. Press the keyboard combination Ctrl+O and after that press Enter to save the speech-dispatcher file. Press the keyboard combination Ctrl+X to exit nano.

You can still toggle enable/disable the screen reader after it has been turned off systemwide by using the keyboard shortcut Alt+Super+S

Maybe "orca" has bean launched. Kill the "orca" (Screen Reader) process, then you should hear "screen reader off".