Hello Vidya,

You have not mentioned about the Exam name for which you want to know the medium of exam.

But words like Mains, GS suggests that you are talking about UPSE Mains exam. So, based on that I'm providing information.

Yes, you can write UPSC mains in Kannada Language. But UPSE Prelims will be in English/ Hindu and Kannada language will not be there.

To get more information about UPSC Mains exam pattern, eligibility, etc go through below mentioned link.

https://competition.careers360.com/articles/upsc-ias-exam-pattern

May this information was useful to you.

Best of Luck!!