Bitcoin is already a global currency.
Is it the most used ? No. Is it largely acceptable ? No, but its adoption is growing.

But if both parts want, it is easy to transfer bitcoin to anyone anywhere in the world.

I don't think bitcoin is competing with other currencies.  It is just an alternative, for people who wants more freedom and don't want to be exposed to governments agendas.
[/quote] Agreed and adding that Dollar is the global currency in fiat which is based on the value of gold and demand. Hence, in crypto currency market, the Bitcoin is a global currency, but the base of Bitcoin may only be demand. So I think that Global currency requires stable position which Bitcoin does not have. Notwithstanding, in cryptocurrency market, Bitcoin is the Queen of coins.