We have seen British people getting RFEs for not translating their ENGLISH marriage or birth certificates. Resend the certificate and write a very short explanation that it IS in English - If the English part is on a second page I would also make sure to make an extra copy of that particular page and add that as well, on top of the certified one. In my country we don't have birth certificates for instance, so I made very sure to put post-its on the "extract from the population register" where it said this is the ONLY "birth certificates" we have in Sweden. It's USCIS after all, they often need things explained to them in a very clear way.