a British protectorate and merged with India following a referendum in 1975. Sikkim has 11 official languages : Nepali ( lingua franca ), Bhutia , Lepcha (since 1977), Limbu (since 1981), Newari , Rai , Gurung , Mangar , Sherpa , Tamang (since 1995) and Sunwar (since 1996). [ 7 ]