3166 code IN-SK HDI 0.684 (medium) HDI rank 7th (2005) Literacy 76.6% (7th) Official languages Nepali ( lingua franca ), Bhutia , Lepcha (since 1977), Limbu (since 1981), Newari , Kulung (Rai) , [ citation needed ] Gurung , Mangar, Sherpa , Tamang (since 1995) and Sunwar (since 1996) Website sikkim.gov.in