https://en.wikipedia.org/wiki/Legality_of_bitcoin_by_country_or_territory
and you'll see that most countries(read governments) are not hostile towards its usage. Only some of them, like China, India and Russia, have some legal restrictions on usage of Bitcoin, but in fact one can say that BTC is legal there. There is a really small number of countries where Bitcoin is totally illegal, and Vietnam(where OP lives) btw do not belong to that number. I think making cryptocurrencies illegal is ridiculous in the modern world, because it's obvious that there's no future without crypto. But people who make laws in some countries are far from being perfect and that's why sometimes we have ridiculous laws. For example potatoes were illegal in 18th-Century France for 24 years. I think in the future everyone will be laughing at past illegality of Bitcoin in the same manner as we are laughing today at illegality of potatoes.