After nearly a decade of trying, Wal-Mart never cracked the country — failing to become the all-in-one shopping destination for Germans that it is for so many millions of Americans. Wal-Mart’s problems are not limited to Germany. The retail giant has struggled in countries like South Korea and Japan as it discovered that its formula for success — low prices, zealous inventory control and a large array of merchandise — did not translate to markets with their own discount chains and shoppers with different habits.