SpeakBird Free

Free (ads) version.

SpeakBird supports two modes:
Notification: as soon as new mentions appear, you will be able to click a notification and a voice will read the tweets.
Speak-as-Pull: as soon as new mentions appear, a voice will read the tweets

The first mode also supports the following options:
-Speak to warn of a new notification
-Switch automatically to the Speak-as-Pull mode if the headphones are inserted
-Switch automatically to the Speak-as-Pull mode if you're listening music or playing

Other options:
-Show a notification when SpeakBird is speaking
-Force the voice to use a language other than the voice system

Open Source (GPLv3) https://github.com/monossido/SpeakBird

Coming soon:
-Automatic detection of the language of each Tweet
-Push