Thanks!
I had never heard of Magomobil before but the big clue for me was the name of the tyres! I discovered it was related to Hungary, but at the same time the flag before the grill was not the flag of Hungary. Nevertheless, I kept on looking for Hungarian car manufacturers until I found out about MAG and immediately recognised that particular -and beautiful- radiator shape. Then I searched some Hungarian car-related websites and heard about some racers made by MAG (or Magomobil) around 1926.
Regarding the flag: I believe it might be the MAG emblem or logo.