As we all know that bitcoin now are being made as a trading pairs to different fiat money all over the world. And we you go round the world having a good vacation on different countries you do not need to bring more fiat or physical money instead bringing gadgets and connecting to internet is enough to get fiat money after it will be traded to local exchange. In this way there is no need for one to bring more physical money as bitcoin could unify all fiat money around the world as trading pairs.
Unfortunately, bitcoin is not going to be something that will be able to unify fiat currencies.
For fiat currencies to come together, there needs to be a world central bank or world government which at the moment is not a thing yet. It might change in the future, but such change comes centrally, since the decisions of governments are entirely out of the control of bitcoin or the bitcoin community itself.
If you're asking the question of whether bitcoin can become a global reserve currency in the future and be used internationally, it already somewhat is. I think adoption growing will help its usability and P2P trading internationally, leading to more convenient transactions. If we see a sufficient market cap and adoption, we may even see institutional investors and potentially governments using bitcoin as a reserve currency, on top of average users using it to transact globally without added fees. It's a definite possibility, and I'd say probability as well.