It only accepted payment in some countries. So Bitcoin is considered a world currency that is very unlikely.
No, we are at early stage of that kind of adoption; few countries are having norms which are friendly to bitcoins whereas most countries are neutral against bitcoins which means people need to stay safer on this own responsibilities; it means we are slowly moving toward the stage of one world currency regardless of where our governments stand against crypto currencies. So, in the near future people may ignore all other payment systems and may adopt bitcoins for worldwide transactions; which will simply emphasize that we are having one world currency.
But, there would be unlikely situation for bitcoin to be declared as one world currency or as worldwide a medium of exchange. Because we cannot expect governments to be convinced before most of world population will be adopting bitcoins. Only based on demand from public, governments start think about it.
I guess the situation will change! The world is making progress in every way, can we even imagine the world in the next 50 years? If you turn around and try to realize the last 50 years, you will find it almost impossible to predict what can happen!
My perspective is simple, if you can imagine one global currency, what that currency needs to be, and what needs to have to take that spot, only Bitcoin fits all criteriums! Without a country that can claim it or control it... is there any other currency that can be accepted by the east and west, whites and blacks, and you name any other difference between countries and people! Bitcoin can solve some trust issues here, simply we need a wallet address and we will know can we trust someone or not!
I believe in one world currency, but that will come when people of the world unite... and that can happen, but when? On which level people's awareness has to be for that? Well, I can only believe that Bitcoin can help all of us in that way, it's a tool, I hope we will learn how to use it!