The majority in El Salvador and 90% of people in the Central African Republic do not have access to the Internet. In both of these countries, bitcoin is now legal tender. But bitcoin can not be a practical currency if people can't use it.
I assume the legal tender is definded as Bitcoin the way we know it, and not as Bitcoin in the form of some printed piece of paper that can be traded. That would make it some private form of money instead of legal tender.
It could work:
~ the Bitcoin Standard: let's take El Salvador as an example, and let's assume they implement a Bitcoin Standard. Instead of holding 10 tonnes of gold, they hold 19,348 Bitcoin (worth about the same as 10 tonnes of gold). The can now issue banknotes, let's call them ElSalvos, worth 19,348 Bitcoin. If they issue 1 billion ElSalvos, each Elsalvo is worth 0.0193mBTC. At the El Salvador Central Bank, you can exchange your ElSalvos for Bitcoin if you want.
But this assumes a trusted party (and a government is trusted by force), and there's no need to print private keys on banknotes.