In essence, Bitcoin is already a global digital currency. Because Satoshi created it intending to become a p2p currency, not a store of value or a speculative asset.
Price volatility can also be considered a major barrier to the use of Bitcoin as a method of payment. But in my opinion, that is not the real reason. The real reason lies within ourselves, most of us do not want to use it for that purpose. Government ban, price fluctuation, high fee or slow speed...these are all just excuses.
Bitcoin was created for a borderless transaction blockchain, and till now everyone can use it like. There is only legal barrier created by governments in order to minimize access of their citizens to Bitcoin blockchain and make their citizens fearful about possible legal issues when using bitcoin for money transactions nationwide and worldwide.
It's legal and psychological challenge for many companies and individuals but it's not enough to prevent all people using bitcoins and certainly not enough to kill bitcoin.
Governments are also one of the barriers preventing the use of Bitcoin as a method of payment. However, I still believe that we ourselves are the biggest obstacle. Because many stores and businesses still accept Bitcoin today. Therefore, it is actually not difficult if people really want to experience or use Bitcoin as a means of payment.
Or El Salvador is a clear example showing that even when Bitcoin is accepted as legal tender. People there still do not want to use it as a payment method to replace fiat or traditional payment method.