I had created a custom TTS solution sometime back as the TTS was not available on early releases of HA.
I am using PicoTTS, which is one of the good offline TTS engine I came across so far.
Here is the demo: View Demo
In the demo, the TTS is for the motion detection sensor. (My custom Microwave Radar Sensor using MySensors node)
Iām happy to share the details if anyone interested
Also see my Grandfather Clock Chime implementation Here