Most of the local people that are above 40-45 years old do not speak English at all. I suppose that it results form the former GDR-times when the people were forced to learn Russian. If you go to Potsdam, be prepared to use some important German phrases: in banks, in the administration services or in the bars. The Civil service in the Rathaus operates perfectly and everyone there speaks English; but in the banks wasn't like that...
In Potsdam, like in all Germany, there is no any free wi-fi internet. You can find internet in some of the cafes or restaurants, especially around Brandeburger Strasse. Otherwise you could buy a T-mobile card for access which is 5 euro per hour (but it is accessible only at some pulbic places).
There's still some run down looking housing near the centre of the city and around the train station, but the place didn't feel threatening at all. Well it's Germany. The place was friendly and relaxed and it doesn't have a reputation for trouble.
If you are standing in the middle of nowhere, having already walked 4km because you missed one bus by 5 minutes and had another 35 minute wait for the next one - and you're standing 10 meters from the bus stop taking photos of a tower that you aren't really interested in - BE CAREFUL! The bus may arrive while you are fiddling with your camera and drive straight past you because you are not AT THE BUS STOP!
Now... if you were a bus driver.... and you were driving along a looooong stretch of road with NOTHING but woodland on either side for miles and miles ... and there was a woman standing a few meters from the bus stop ..... wouldn't you think "Hmmmm... maybe she wants to catch a bus???" You would think that wouldn't you??
But No..... I wasn't exactly AT the bus stop.... and this is Germany ... so the driver wasn't stopping. I should have looked up sooner but thought I had a few more minutes before the bus was due - he was EARLY! Silly me for taking boring photos. I had another 2 km walk to the train station. Suffice to say I wasn't best pleased!
It costs a little more to travel to zone C where Potsdam is to be found.
Don't get caught out it could cost you €40. Make sure you have paid the extra!
Its truly worth going to visit Potsdam.