Making Bitcoin a legal tender means when a person goes to purchase a commodity, instead of paying with dollar or whatever currency is being used, they pay with BTC.
If bitcoin is legal in your country, you can still use bitcoin to make transactions and purchase commodity legally. It doesn't have to be a legal tender for merchants to accept bitcoin but they can also decline if you pay them with bitcoin. But if it becomes a legal tender, than a merchant must accept bitcoin when it is offered as a form of payment.
Given the unstable nature of cryptocurrencies, and the untraceable nature, would you suggest it wise for countries to adopt Bitcoin as a legal tender?
Bitcoin is unstable, but much more stable compared to other altcoins. But you are wrong here if you think bitcoin is untraceable in nature. Bitcoin isn't anonymous. It is pseudonymous and can always be traced back to you.
Recently, El Salvador and Central African Republic announced that they have adopted Bitcoin as a legal tender.
They already did. El Savador was the first country to make bitcoin a legal tender.