I kind of solved the problem for me and myself only.
There are two components to this: 1. the actual hardware wifi-speaker, and 2. software to support it.
I happened to have an old sonos speaker lying around in the house which no one uses. I end up used that as a wifi speaker
Software wise, I have send a feature request to the development team (I think) to incorporate picotts (a very basic text-to-speech engine) into home assistant. I am not sure what is the proper channel and I have send request both here at the community website and the github. I have not heard anything from the developer yet. You can take a look at my request here, and if it is something you like, please vote for it in attempt to grab developer’s attention:
While waiting for the developer to act, I made a custom-made home assistant docker image (for 64bit x86 machine). If you happened to run home-assistant in a docker and use a 64bit x86 machine as host, you can download the image here:
docker pull kngharv/home-assistant:picotts
If you use something else, you can try to custom build home assistant image yourself. It is really just add the picotts library to home assistant distribution at the OS level.
Right now, I am trying to figure out how to leverage this LAN-based audio alert as part of my automation scenario.
Good Luck