Can I translate Koine Greek into modern Greek into English?
I suppose you could translate from one language to another language to English. But why would you want to do the extra work? Aside from that you may run into issues as you translate. For instance, even though it’s the same language Koine Greek has different meanings even from the same words than modern Greek.
So a word may have a slightly different meaning or range of meanings between the two eras of the language. This could produce a wrong translation in English. It’s an extra step to go from Koine to modern Greek. Why not just go from Koine Greek to English?
Even though it’s within the same language there are hundreds of years between these two languages. One is a dead language and the other one is a modern living language. There’s a lot of change that happens in English even over the last 15 to 20 years, let alone hundreds of years for Greek.
I would counsel you to just go from Koine Greek to English. You don’t have to worry about making sure you choose the right word or range of words. Your translation will flow better if you don’t have to figure out whether or not the word is accurate to the time period.
If your audience was a completely Greek audience, they would be no need for the English translation. You want to translate from whatever time period in Greek you are translating from.
If you are translating from the New Testament it is better just to go from Koine into English. If you are translating from modern Greek audience can go from Koine Greek to modern Greek. The less languages you involve in your translation process the better. Involving other languages and even other times in those languages changes the meaning significantly.