Does anyone know why during mass, we continuously switch from Coptic to Greek? For example, during the 7 short litanies, the priest only uses Coptic but all the deacon responses (except for the one for the air and heaven...) is in Greek. Or during the Confession, the deacon's reply (Amin, amin, amin, tinati, tinati, tinati...) is in Coptic and then switches at the middle to Greek. There are countless other examples during mass and I don't really see a pattern for the switching.
Why are there these switches and why do they occur specifically at these spots? Are they vestiges that were kept from the Egyptian era of Greek-Coptic bilingualism?