bitcoin has already been a global currency since it was first created. Satoshi waant people to use this coin as a primary school on the global and this coin is a symbol of the crypto currency revolution
Perhaps still not as much globally as you think. Because the fact is that only a certain number of people use crypto currency and there is no talk of mass use of speech.
Where to find relevant numbers of usage ? It is possible to know the order of magnitude of how many people own bictoins but it is important to know how many use bitcoins per day and per month : monthly active user and daily active usage.