Complex sentence: For over forty years, "La Grande Vadrouille" was the most successful French film in France of all time, topping the box office with over 17,200,000 viewers in cinema until 2008, when "Bienvenue chez les Ch'tis" attracted over 20,000,000 cinema-goers.
Split into simpler sentences: For over forty years, "La Grande Vadrouille" was the most successful French film in France of all time, topping the box office with over 17,200,000 viewers in cinema. It finally lost that distinction in 2008, when "Bienvenue chez les Ch'tis" attracted over 20,000,000 cinema-goers.