See you travel doctor. Some are courses of 2 or 3 injections so allow time for this. Currently certificates of inoculation against Yellow Fever and Cholera are not required except from visitors arriving from countries where those diseases are endemic. Local police will give you copy of report if necessary. Rural people may speak some English.
National languages are Swahili and English.
For the more rugged, Omo is the local soap. Drying in the sunlight is fast. The drug is taken before, during and after the trip. Malaria is transmitted by mosquitoes. Mosquitoes are only a problem at sunrise and sunset and at the lower altitudes.