Bhutan is linguistically rich, with over nineteen dialects spoken. The richness comes from the geography: high passes and deep valleys forced the inhabitants to live in isolation, which also contributed to their survival.
The national language is Dzongkha, the native language of the Ngalops of western Bhutan. Dzongkha literally means the language spoken in the dzongs, the fortresses that serve as administrative centres and monasteries.
Two other major languages are Tshanglakha and Lhotshamkha. Tshanglakha is the native language of the Tshanglas of eastern Bhutan; Lhotshamkha is spoken by southern Bhutanese of Nepali origin.
Other dialects include Khengkha and Bumthapkha, spoken by the Khengpas and Bumthaps of central Bhutan; Mangdepkha, spoken around Trongsa; and Cho Cha Nga Chang Kha, spoken by the Kurtoeps. The Sherpas, Lepchas and Tamangs in the south have their own dialects too. Two, Monkha and Gongduepkha, are close to extinction.
English is the medium of instruction in schools and is widely spoken, so you will manage perfectly well.