Time travel to the future is interesting but not harmful. Time travel to the past is disastrous. But no one had concept if it do you'd be free to overwrite the future.
You've got it. In 500 years we'll never advanced so much and there will have been so much current exchange and drift I doubt you could be understood at all.
In the 1500s you could get by as a foreigner who barely understood the language. You'd have zero cultural norms so most language that wasn't literal would be unintelligible.
That is wrong. Stochastic yes. Photons emission is probabilistic. Destructive interference causes emission to overwhelming follow classical wave theory. Here's a better explanation with a neat graphic.
That's light as an aggregate wave. Photons, actual light, always travel at c. What's happening in a medium is the rapid absorption and readmission of photons. The probability of admission is based on structure of material causing things like lens or mirrors to work.
You can think of it as the photons having to jump between platforms before the can continue running at c.
Don't think about individual photons. Think about billions of them with destructive and constructive interference. The probabilities of all the sitting l additive waves of light.
That's actually a myth. Glass is an amorphous solid. It exists the Glass Transition, which is where the solid changes from brittle to rubbery as it heats and begins to melt.