While there are ways to get your Arduino, Raspberry Pi, BeagleBone or ESP8266-based project to speak, for an easy near-universal solution it would be hard to imagine something better than this TextToSpeech board now funding on Kickstarter. It features 7,000 English words spoken by a real live human, plus the option to instead use 20,000 words in robo-glish, or 10,000 words in robo-German, or 10,000 in robo-French as well.
Besides an impressive vocabulary, probably the coolest feature of this device is that the interface is simply a serial connection. This enables dev board communication with only a Tx output, and there’s a level shifter that lets it work with 5V or 3.3V as needed. It can even connect to your computer via USB, letting you command it to speak words via a serial terminal — such as the one built into the Arduino IDE.
Output-wise, the TextToSpeech board sports connections for a 3W speaker with a trimmer pot for the volume, along with a line-out connection and headphone amplifier. Finally, while speech files are included, you can also add a .WAV file to the SD card to allow it to play music, a prerecorded sentence, or combine it with other words emanating from its stored audio library.