Answer
Obtaining a birth certificate through an interstate request usually takes 6 to 12 months. This is because the Russian civil registry office sends a request to the relevant country to determine whether a civil-status record exists.
After receiving a response from the competent authority in the other country, the civil registry office issues the birth certificate. If the record is held in another former Soviet republic, the document is issued by the country where the record was made, not by a Russian authority simply because of the applicant's citizenship.
This route should be planned with plenty of time to spare. In addition to waiting for a response, allow time for delivery, an apostille in the country where the document originated, translation, and further preparation. If the document is needed by a particular filing date, it is best to start the interstate request as early as possible.