Hey there

Yes you are eligible to write union Public Service Commission exam in Hindi language if you are facing difficulty in writing the exam in English. You can give both prelims and mains exam in Hindi language. However there is one paper "English" which you have to write in only English language. UPSC also provide the facility of taking your desired language while giving interview of UPSC.

For more details:

https://www.google.com/url?sa=t&source=web&rct=j&url=https://competition.careers360.com/exams/upsc-civil-services-exam/amp&ved=2ahUKEwjk5siggbbzAhV1RvEDHaeaAAIQFnoECAkQAQ&sqi=2&usg=AOvVaw0YgHjPSGbCBqWgNlDAT28h&ampcf=1