Bitcoin can't become a global reserve asset like gold unless it's backed by rich countries. El Salvador's a small country it's decisions don't affect other countries. If BRICS G8 or G20 want to make bitcoin a global asset it's possible.
The US government recently established the Strategic Bitcoin and that marked a significant shift in the country's federal cryptocurrency policy. If the world's largest economy can launch such initiative through an order signed by the county's president himself, then what makes you think Bitcoin can't become a global reserve asset? The truth is that Bitcoin is gradually dominating the global finance system so you shouldn't be surprised if more governmental bodies adopts the policy