The military censor in Israel does the exact same thing: ostensibly to prevent enemies from using the data to improve their systems, in reality as an attempt to keep domestic morale high (it only ever manages to slow down the inevitable fall, though).

Not really, it’s still fully FOSS, they were just terrible at communicating what they actually wanted to do and people got spooked.

Yes, but it’s usually very subtle (e.g. in realizations of single phonemes or in intonation). There are also more extreme cases which other commenters have pointed out.

I recommend you look up sociolects and sociolinguistics.

Was reminded of this article if you’ve got some time to read