Bitcoin is definitely a legal currency,but its legality ultimately depends on your country of origin/residence...
Few countries have actually cracked down on the system and stopped all its activities by their citizens and within their jurisdiction
So try finding out if your country is one of them,if not then you're free to start trading on the bitcoin and other crptocurrencies
Good luck
bitcoin before being exchanged for fiat currencies in the digital world, or the internet world is a borderless world, we can be sure we can trade without using our home country, so everything in cyberspace is legal, but after we exchange bitcoin into the country of origin of the currency we, this is what starts making bitcoin traders start to intersect with the systems of each user's country, but as long as we trade in the virtual world as long as it's legal, bitcoin is not touched by any law.