The use of cryptocurrency is has increase over the years as many people now see crypto as an alternative to the fiat. My question is if the government legalize cryptocurrencies are means of payment, what will be the implications on the global economy?
Crypto is an addition to fiat not an alternative. For being an alternative, majority of merchants would have to start accepting it, that stage is far from our reach at present. Since you are in this forum with bitcoin-users it might seem that crypto is popular, but come to the reality, in most countries you will rarely come across a bitcoin user in the day to day life.
Governments have not legalized crypto in many countries yet, so it is hard to predict - but considering the model on which bitcoin is created, it will be for the good, inflation should reduce and corruption/bribes should also stop.