You mean like making it a national currency?
I don't think BTC will be solution for African Governments, but to African people.
Small investors could just buy bitcoin to stay away from country's inflation problem, for example.
How will locals with no access to foreign currency buy BTC in the first place?
In local exchanges, ofc.
Just buy bitcoin from localbitcoin, from local exchange with the local fiat and so on. There are certainly many people with bitcoin in africa who are willing to sell them in exchanges.