Why choose a single currency? Just return to gold standard, values of goods and services denominated in mg, g, kg of gold. Most international trade is already

Why choose a single currency? Just return to gold standard, values of goods and services denominated in mg, g, kg of gold. Most international trade is already done electronicaly, so there would not much need to physicaly move gold. Goverments don't like gold standard because they can't print gold.