Hello aspirant

Generally the UpSC paper is printed in two languages for preliminary exam. , One in Hindi and other in English.

In mains exam there are two papers compulsory one for English and other one language that are mentioned in constitution schedule 8.  You have to qualify both the papers . And  In case of other paper you can choose your language of the examination like  Hindi, English or any other languages for writing HS mains and optional easy papers.