[DarylZero]

Even having a separate, but integrated, internet-connected voice recognition system would allow the devices themselves not to be internet-connected.

This is possible on Android, you can have an Android app call out to Google for voice control, and have the app control your local network.

[krisoft]

That is in fact how most smart lights are implemented. There is a central unit each lightbulb connects to and that central unit (optionally) is connected to the internet.