Is the Birth Certificate you submitted just a letter pad from KTM ward office ? If so, that's not a proper Birth Certificate. USCIS sometimes doesn't seem to accept that. In Nepal they have a formal Birth Certificate (written in Nepali Kagaz) which is written in Nepali (at the top) as well as English (at the bottom). So, the real Birth Certificate doesn't Need any Translation.

Try to get a real Birth Certificate, which is usually issued by ward office you were born in. It depends on whether or not your birth is registered. If it's already registered, no issues. They can issue a formal Birth Certificate. It'll be in English and Nepali.

It should look something like below.