The official language in The Gambia is English. It is spoken in Parliament, at the administration of justice and at all official events. The language is taught at school and it rarely happens not to have somebody around who has a little command of the language. In the inland that might happen to you, but that should be an exception. In tourist areas everybody speaks English of course. However, keep in mind that education has never been compulsory in The Gambia, so there are a lot of people, particularly among the elderly, who can not read and write. French will serve you in most hotels as well.
The Gambia doesn't differ from other countries at all: people get madly enthousiastic if a foreigner speaks a few words in their language. Considering the amount of languages in The Gambia a rather impossible task. But do remember:'Na nga def?', 'how are you?'. Then you say:'ma ngi fi rekk', 'I'm fine'. Inland you will be greeted with:'asalaa malekum', 'let peace be with you'. The answer: 'malekum salaam', 'and with you and your family'.
There are small booklets available at TravelPoort Gambia translations of simple words and sintences from English into Wolof and Mandinka. A set costs 10 Euro, including the mailing to Great Britain.