While there are a number of things that could be causing this, I would first try this:
Go to settings>Apps(or Application manager)>Find the Text to Speech/Speech to Text engine
(Depending on your phone, for the above instructions when you scroll to the Text to Speech (TTS) in the apps list prior to clearing the cache and data look for "Google Text to Speech Engine", "Pico TTS", or anything that says "Text to speech", "TTS" or similar).
You then may need to click on "Manage Storage" depending on the Android version you are using. Clear Cache and Data at this point and restart the phone.
Hopefully that works for you, but if not-- provide some additional details about your phone so that myself or someone else can better assist you
Talk to text is an incredibly useful feature. I don't want to see you unable to enjoy all the great things your phone can do. What happens when you try to use talk to text? What phone do you have? Can you think of any changes around the time this started?
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