Hello,
the poor areas of german citys at this times had been the old, historical parts (downtown / Altstadt). This houses had been framework buildings. Low rooms, no toilets, no central heatings, overcrowded. The streets had been small and dark, because the houses got 4 to 5 floors, and they tend go got more wide at their upper floors. Terry Pratchet use the term: the shadows. Very good.
This areas in nearly all german citys are lost. They burnt down to the ground during the WW2. After the war this areas get a reconstruction. Today they look compleatly different.
Yes, there are complete framework downtowns in germany, but this are not the big ones, not the "slums". At the smaller town the situation was different, not so precarious (for the poor people).
Berlin is a different thing, this city expand late (1860 ?), there big brickstone houses with many little floors and small rooms were built.
Yours, Sebastian