Russians prefer their Lay’s potato chips dusted in caviar and crab flavors. The Chinese like their Oreos stuffed with mango and orange cream. And in Spain, Kellogg’s All-Bran cereal is served floating in hot coffee instead of cold milk. Americans might get squeamish at the thought of their favorite snacks being tweaked. But what works in the U.S. doesn’t always work everywhere. In other words, Lee Linthicum, a market researcher, says: “It can’t be some generic mix of spices that might fool an American.’’ Food makers long have tinkered with their products to appeal to regional tastes, but getting the recipe just right is becoming more important than ever. That’s partly because people in developing nations such as China and India are gaining more of an appetite for American-style “on-the-go’’ foods as they work longer hours and have less time to cook. But it’s mostly because snack makers increasingly are looking for growth in other parts of the world as sales slow at home.