I showed this cartoon by Peter Brookes from The Times to a group of adult students this morning. Of course, they knew it was a cartoon about Brexit, but not one of them was able to identify the main reference. What about you? (see below for explanation)
The cartoon references the 1965 hit movie musical The Sound of Music, which tells the story of a young Austrian woman, Maria, studying to become a nun in Salzburg in 1938. She is sent to the villa of a retired naval officer and widower to be governess to his seven children. After bringing love and music into the lives of the family through kindness and patience, she marries the officer and together with the children they find a way to survive the loss of their homeland (to the Nazis) through courage and faith. In the cartoon, Theresa May is shown in the role of Maria, giving the finger (an insulting gesture) to three prominent EU leaders: Jean-Claude Juncker, President of the European Commission, Angela Merkel, and François Hollande, who are portrayed as children. She's wearing a Union Jack skirt or apron, and singing one of the songs from the movie (watch it here). The caption is 'The Sound of Madness'. Click here to see the image on which the cartoon seems to be based.
The cartoon relates to Mrs May's Brexit speech on Tuesday in which she said that the UK would be leaving the EU Single Market. The cartoonist clearly thinks this is not a good idea, since he describes it as 'madness'.
'So long' and 'farewell' are two ways of saying goodbye. 'Auf Wiedersehen' and 'Adieu' are German and French for 'goodbye'. See here for an article on ways of saying goodbye in English.