Maybe this helps Assange from not getting extradited since this is clearly against international law and many places will not extradite you to a place that commits theses kind of crimes against it's prisoners.
Quite honestly, no person should ever be extradited to US prisons, no matter for which crime. The utterly inhumane conditions in US prisons are well-known and well-documented. Many US prisons are engaged in massive and habitual human rights abuses. On a side note, in my experience only people from the US habitually make "don't drop the soap" prison rape jokes.
UK has made it very clear that they are not among these places.
They're going along with the abuse, with all the subtlety of an 8 year old girl bully. "Oh, you thought we would care about such things as honesty and decency when it came to you?"
Anyone who's followed the Assange case has seen that little game played out over and over: give him a faint hope that the nightmare will end, then snatch it away with a smirk.
There’s really nothing in the letter that sounds like anything except normal jail.
There’s something about 24 hour “speakers” which sounds alarming, but if it were what you think it sounds like he would have elaborated on it a lot more. There are also a lot of people “speaking” in these places 24 hours a day which can be frustrating.
Other than that this looks like deranged whining to me.
You act very confident without proof. There are documentaries of the torture styles the US government used. Speakers that will blast white noise. Sleep deprivation will literally make you go insane.