As an evidence we suppose to submit birth certificate while filing form I-485 but my birth certificate is in neplai. Any suggestions what should I do?

You can request from Nepal. Most can email you the birth certificate from Gaupalika or City. They have template in English as well. I got mine last week in English . I never had one.

I recommend getting the new version of it, which is on both english and nepali language on it . I submitted the full "nepali copy" with a copy of translated one, they didnt accept it and made a new one with both language on the original copy and submitted and they accepted

Certified notary public in Nepal also certify the translated version.