Hi Nandita, UPSC does not very much focus on the language proficiency rather it wants good candidates having knowledge, attitude and skill. The journey of UPSC is divided into 3 parts prelims, mains and interview.

As far the language is concerned one can give exam in nay language that are mentioned in the schedule 8 of the constitution. In the preliminary exam the paper is generally printed in two languages one is Hindi and other is English . Where as in the mains exam there are two compulsory papers one for English and other for one language that are mentioned in the constitution schedule 8. You have to qualify both the papers. And in the case of other paper you can choose your language of the examination like Hindi , English or any other languages for writing GS mains and optional and essay papers.

Similarly in the personality test also you will have the option to give your interview in the language you want to like Hindi , English, or any other languages that are there in schedule 8 of the constitution.

hopefully this helps.