It's already an international currency not only because of population because compared to the world population, its still low but because of the fact that I can exchange with anyone around the world in a matter of minutes and it's settled the point of acceptance is where the issue is where I don't have to convert to fiat to rent an apartment or buy food in an eatery or even pay for transport. It's really something I'm looking forward to.
The hard thing about defining Bitcoin as an international currency is the fact that we don't know th real definition of what an international currency is. But from what I know the closes thing to an international currency is Euro in which is the European countries use in their daily transactions. Yes it is an international currency but I don't think it can be called as a global currency. Bitcoin is perhaps something in between as we don't have a proper data for Bitcoin.