I can't believe that I've still never been to Germany, despite having been to pretty much every other country in Europe now. I've even been at the border with different country like Italy, Holland, Czechia and Poland, with Germany just across some road or bridge, but just never entered Germany. I hope to finally visit one day.
Those double-decker trains are quite standard on the mainland. I wonder why we don't have them here.
You should go. Berlin is fun and most people speak English. I think Magdeburg is off the tourist trails, so you saw less English signs.
The UK rail network is old and most of our tunnels cannot take bigger trains.