There currently is one option to travel by night train from Odense (Denmark) to Děčín (Czech Republic), taking approximately 9 hours: Namely the RJ 387. These lines are operated by DSB and Deutsche Bahn.
DSB (Danske Statsbaner) is Denmark's national railway company, operating passenger trains across Denmark as well as connections to neighboring countries.
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.