Hi,
UPSC Prelims are held in two languages in India which are English and Hindi. The question paper is in both these languages.
Since prelims is a MCQ based paper so the students do not have a choice but to follow Hindi ir English languages.
But for the mains students can choose a language mentioned in the 8th schedule of constitution.

Sandeep, UPSC Prelims exam is conducted in 2 languages. In Hindi and English. Regional Langauages have not been included yet. The exam has Objective Multiple Choice Questions only. So if you can prepare smartly, you can ace the prelims.

UPSC is a 3 stage   selection process involving Prelims, Mains and Interview which tests your personality test. Prelims has 2 Papers namely General Studies and CSAT.

General Studies has Current Events, History of India and Indian National Movement, Indian and World Geography, Indian Polity and Governance, Economic and Social Development, Environmental Ecology, Biodiversity and Climate Change and General Science.

CSAT has Comprehension, Interpersonal skills including communication skills, Logical Reasoning and Analytical ability, Decision making and problem solving, General Mental Ability, Basic numeracy and Data Interpretation.