First of all, the synopsis on Google stated it's a WWII. story in Germany.
In case some potential viewers are not aware, it takes place in Budapest, Hungary, partially during the Nazi German occupation of the country, NOT in Germany.
As far the title song "Gloomy Sunday" goes, it was composed back in the 1930's in Budapest by a Hungarian composer and musician.
All that said, it is a good story and movie about the so-called "Hungarian Suicede Song" that, reportedly, inspired many cases of suicides in Hungary and around the world, INCLUDING that of THE COMPOSER himself...