Your mistaken bitcoin is already a global currency considering that most of the world population is using and has knowledge about it, some even invested in it. And not a single individual can control the price of it cause it's a decentralized currency no one owns it. Not even the devs because without it's users they have no job right now.
Indeed, in every country in this world there will always be bitcoin users. But it doesn't mean everyone (all human) in this world uses bitcoin. The OP said 'global currency' so that's meant is everyone in this world accept and use bitcoin. And now to make bitcoin into global currency will be hard to realize. Government regulation and the characteristics of bitcoin is not suitable for use as currency. Bitcoin users will prefer bitcoin as an investment place, they are ralely use bitcoin as a means of payment.