Men are advised to wear a collar and tie and women to wear smart, business-like dresses or suits. If meeting business contacts on a social basis, it is possible to dress more casually but not too casually.
Do they still dress traditional once or in some parts?
I think in some areas yes and dashiki is a colorful garment that covers the top half of the body, worn mostly in West Africa. It is also known as a Kitenge in East Africa and is a common item of clothing in Tanzania and Kenya. It has formal and informal versions and varies from simple draped clothing to fully tailored suits.