Bitcoin is a digital currency that has a global function because it can be used as means of payment transactions in various countries.
except in some countries prohibit the existence of bitcoin
And if bitcoin users will be found in every country of the world. Then that's the start to call bitcoin as a global currency and most of us are coming from different countries and I guess this is enough to treat bitcoin as a global currency. And right now with the news that Japan is trying to adopt bitcoin which makes it another achievement for bitcoin.
Japan has already adopted bitcoin as a main currency and that is great step to make bitcoin even more popular and that has drawn attention of many other countries and we can expect that those countries will also start following Japan in coming time.