The country's principal language is Kinyarwanda, which is spoken by nearly all Rwandans. The major European languages during the colonial era were German, though it was never taught or widely used, and then French, which was introduced by Belgium from 1916 and remained an official and widely spoken language after independence in 1962. Dutch was spoken too. The return of English-speaking Rwandan refugees in the 1990s added a new dimension to the country's linguistic diversity. Kinyarwanda, English, French, and Swahili are all official languages. Kinyarwanda is the national language while English is the primary medium of instruction in secondary and tertiary education. Swahili, the lingua franca of the East African Community, is also spoken by some as a second language, particularly returned refugees from Uganda, Kenya, Tanzania, and the Democratic Republic of Congo, and those who live along the border with the DRC. In 2015, Swahili was introduced as a mandatory subject in secondary schools. Inhabitants of Rwanda's Nkombo Island speak Mashi, a language closely related to Kinyarwanda.