The chief ethnic groups are the Hutu and the Tutsi, who traditionally comprised 84 % and 15 % of the population, respectively. due to Hutu emigration and Tutsi immigration, the politically dominant Tutsi now make up around 20 % of the population. The Twa, a pygmy group, account for 1 %. The official languages are Kirundi and French. Swahili is also widely spoken along Lake Tanganyika.