The main spoken language in Mauritius is Creole (a French dialect) which forms part of the very culture of the island. This is the way Mauritians communicate with each other though other languages such as English, French, Hindi, Bhojpuri and Tamil can be heard. Because of the presence of the different ethnic groups on the island with their different languages and because English and French are compulsory in most schools, most Mauritians can speak more than two languages (usually Creole, English and French).
English is the official language of Mauritius; it is used in all government procedures (though French and Creole can be heard during national assemblies of ministers), laws, businesses etc. English is the medium of instruction in all schools too given that books are in English and it is compulsory up to O level; at A level, English is replaced by GP (General Paper) which is a form of English in a more general way. Though English is of major importance in Mauritius (like failing in GP at A level means total failure!), it is not commonly spoken by Mauritians.
The Mauritian Creole aka Kreol Morisien is something of a unique language in that it has its roots as far back as the 17th century; during that time, when African slaves were taken from their home ranges to work in Mauritius, they could not communicate properly with their masters because of the language problem. They created a language of their own by mixing words from their language with different French words giving rise to Creole. Mauritian Creole is very similar to french except in the way the words are pronounced and with some words having different meanings completely. There are a few published dictionaries in Creole now as the language is gaining more ground as cultural asset of Mauritius.
French is undoubtedly the most common spoken language after Creole. More and more people speak French nowadays and as from very early ages too. It is the language that is used in formal situations like interviews, one on one with unknown people as well as in the media (radio, TV, newspapers). All Catholic schools require that students speak French on school premises. It is also known as the language associated with culture.
Other spoken languages in Mauritius are Hindi and Bhojpuri that can be heard a lot in the villages. They were brought to the island by the early Indians who came as indentured labourers and which has thus been passed on from generation to generation. The Chinese too commonly speak mandarin amongst themselves as well as have their own newspapers in mandarin. Communication is very easy in Mauritius given that many languages are spoken; if you can speak some English or French, you will easily get by.