Nigeria has well over 300 ethnic groups, each of which has its own language or dialect. In such a language-diverse country, English has come to be seen as the unifying language and although the dominant indigenous languages of Hausa, Igbo and Yoruba are widely used they are not universally understood.
You should therefore have no problem conducting business in English throughout Nigeria and certainly all senior governmental figures and business leaders will be fairly fluent in the language.
Nigerians like to use language in a fairly flowery fashion and will often address you with great courtesy and overt signs of respect. This desire to show respect to people is shown in the Nigerian use of titles and honorifics. People will often be addressed as Uncle, Auntie, Chief, Mazi, Doctor etc. rather than by the use of first names. Do not be surprised to hear yourself being addressed as 'Sir' or 'Boss'.
Business conversations will often veer towards the personal and you may be asked questions about family, hobbies and other interests within business meetings. This is an important section of the meeting and should be treated as such. It is not seen as overly personal but rather as a signal of warmth and friendship.
Handshaking is very important and it is usual to exchange long, lingering handshakes with everybody you meet. Do not be in too much of a rush to have your hand released — just relax.