Even though Nepali (written in Devanagari script, the same as Sanskrit and Hindi) was the national language and was mentioned as the mother tongue by approximately 58 percent of the population, there were several other languages and dialects. Other languages included Maithili, Bhojpuri, Tharu, Tamang, Newari, and Abadhi. Non-Nepali languages and dialects rarely were spoken outside their ethnic enclaves. In order to estimate the numerical distribution of different ethnic groups, the census data indicating various mother tongues spoken in the country must be used.

In terms of linguistic roots, Nepali, Maithili, and Bhojpuri belonged to the Indo-European family; the mother tongues of the Tibeto-Nepalese groups, including Newari, belonged predominantly to the Tibeto-Burman family. The Paharis mother tongue Nepali, was the largest ethnic group. If the Maithili- and Bhojpuri-speaking populations of the Tarai were included, more than 75 percent of the population belonged to the Indo-Nepalese ethnic group. Only three other ethnic groups--the Tamang, the Tharu, and the Newar--approached or slightly exceeded the one-half million population mark. Most of those non-Nepali linguistic and ethnic population groups were closely knit by bonds of nationalism and cultural harmony, and they were concentrated in certain areas.