It was meant to mimic the "Golden Age" of Danish erotica, which gained international fame in the late 1960s and 70s for being more "progressive" and "artistic" than traditional adult content. Why People Keep Searching for It
The title was suggested by Gordon-Levitt's cinematographer, who was Austrian and familiar with the history of progressive Danish adult films from the 1970s. Friends with Danish parents helped him with the proper translation and spelling of "Forår for søde Brigitte". Forar For Sode Brigitte Danish Movie -
While you may find references to it online, "Forår for søde Brigitte" (Spring for Sweet Brigitte) is not actually a real Danish movie. It is a created specifically for the 2013 movie Don Jon , written and directed by Joseph Gordon-Levitt. It was meant to mimic the "Golden Age"