Belgian chocolates tend to have a light fruity or floral tone, as a result of the preferred style of light roasting. The chocolate also might taste sharp or even tannic due to both the roasting and the fermentation of the beans.
Italian chocolates may possess a characteristic flavor of brown dried fruits: dates, raisins, even figs. Italian chocolates do not have an intimidating or overwhelming flavor profile and will appeal to most people seeking excellent high-end chocolates.
Swiss made chocolates tend to have stronger overtones of vanilla. They are lighter and smoother in both taste and texture.
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These are basic generalizations but the real differences arise not between the countries but rather the specific manufacturers: Lindt vs Valrhona vs Venchi...
A similar comparison can be made to wines. Alot of different countries produce many varieties of wine, some are better than others but not all Italian wines are the same, neither are all French wines...depends on the vineyard.