The app uses the Android integrated audio text to speech functionality and as a result, it should work without any action. However it may be necessary to install it manually on certain devices.
Please follow these steps on your device:
                                - Open Android Settings
                                - Go to 'System' or 'General management' (Languages, gestures, time, backup) ①
                                - Go to 'Languages & input' ② (this step may be skipped on some devices)
                                - Go to 'Text-to-Speech' or 'Speech Synthesis' ③
                                - Make sure 'Speech Services by Google' is selected or select it
                                - In 'Preferred engine', tap the button on the right (Gear) ④
                                - Tap 'Install voice data' ⑤
                                                                - Choose Chinese ⑥
                                                            - Then you can choose one of the available voices ⑦                        
The labels may be a bit different according to your device/brand/manufacturer.
                                                            IF IT STILL DOESN’T WORK AFTER INSTALLING THE CHINESE VOICE, please try the following:
                                                        
                        
                                - Go to the Google Play Store following this link on your device: Speech Recognition & Synthesis
                                - Uninstall then reinstall the Speech Services by Google.
                                - Restart your device.