Buried in the replies is a comparison with iOS’s on device speech recognition enabled, which paints a somewhat (though not entirely) different story: https://twitter.com/BenLumenDigital/status/12657182691908321...
Unfortunately, airplane mode is the only way to enable off-line dictation. Or, is there another way?
The first version of dictation had no online mode at all; when Apple added that, presumably as a Slowloris attack on the entire world, it ruined the entire experience.
Apple's online, presumably neural network based speech transcription service is horrible. It is an absolute disaster. Slow, unresponsive, drops syllables randomly, and provides no good feedback to the user. It is hard to believe that it was designed by someone who actually intended this product to be consumed by real users. It fails even basic comparisons against the predecessor that it was intended to replace.
Will it contact servers to sends statistics and samples when back online?