March 21, 2016
No longer need to be on 4g or Wi-Fi to use voice dictation: can be offline with no internet connection.
Correction: in the demo I say it just works automatically. However, if your language supports offline voice dictation you may need to turn it on in Settings, General, Keyboard, Dictation on/off toggle. I dont' know why, but my setting was on by default which according to some blogs will be turned off by default.