There currently is one option to travel by night train from Berlin (Germany) to Trzebinia (Poland), taking between approximately 8 and 9 hours: Namely the EC 431. These lines are operated by Deutsche Bahn and PKP Intercity.
Deutsche Bahn (DB) exited the actual night train business in 2016. However, it operates around a dozen Intercity and Eurocity trains that run exclusively at night.
These trains only have first and second class seats. The cars remain lit throughout the night and the seats cannot be reclined.
PKP Intercity, Poland's national long-distance operator, connects cities across Poland and beyond its borders.