How to Talk in Kenya is Simple because Kenya is a former British colony and for that matter English is one of the national languages.
English and Swahili are the two official languages. You can get by with English in the larger cities, and when dealing with those connected to the tourism industry, but outside of that a few words of Swahili go a long way.
Tribal languages, such as Maa spoken by the Maasai, are commonplace in more remote areas. You will still usually be able to find a local who can speak Swahili — although in such areas a guide will be indispensable. Sheng (a slang of English, Kiswahili and local languages) is spoken mostly by urban youths.