It is already a international currency as majority of people across the globe are using it, the only thing we need is that it should hit the mainstream to get more popular in future.
Using it for what? Drugs, gambling, and nefarious activities. No one is using it to buy everyday goods, trust me, and if they are, I'd either question if they have mental issues or just filthy rich.
Buy a cup of coffee with bitcoin? No thanks, I don't want to pay $50 for a cup of coffee.