sorry i don't know what is the purpose for b.c for you but if it's for immi i don't think a translation of nagarika will fly. for complete b.c you need to have facts such as name of both parents, place of birth. i dont think nagarika has that, of maybe it does it's bee a while. checkthis link: http://www.immihelp.com/birth-certificate/

now a days Nepali wada can issue you a birth certificate, some do that even in
English... or you can have it translate and norotize it. if for immi don't forget to send both Nepali and english tranlation together. sorry don't want u to get unnecessary rfe and hassle if it's immi u are trying to do. good luck.