A question for you, and anyone else who might have an opinion ... what's your stance on including other languages in the story? In your case, say it's someone speaking Aramaic or Egyptian. Would you have a note saying they were talking in the language or try to include some words?In my case, Nico doesn't speak a word of Aramaic or Egyptian. Since I'm writing 1st person POV, the best Nico could say is he heard a pile of gobbledygook. If you can't speak a language, it's almost impossible to pick up words from a flowing conversation. As it happens, in the second book there's a scene on the docks of Ephesus in which Nico observes a crew of Egyptians on their boat. He can't follow their conversation but he can tell from the volume, the tone and the gesticulations that they're having chaos.
If I were writing 3rd person POV it would be a different matter. I could POV switch into the head of whoever understands the local language. Alas, I'll never have that luxury, but on the other hand, having the protagonist not understand what's going on has its potential for fun, too.
Nico will probably pick up some Persian over time - many Greeks did, especially Greeks working in trade or diplomacy...or investigation - and when he does Nico will simply say he's speaking Persian and I'll carry on typing English. I'm already writing English to represent what was "really" spoken in Attic Greek. I'm not sure I'd want to try adding Persian in some different way.
It's not quite the same thing, but I do edge a few Attic Greek terms into the stories. The Athenian parliament is the Ecclesia, a water jar is a hydria, the city mayor is the Eponymous Archon, a General is a strategos, a high class call girl is a hetaera. A little bit is great for atmosphere. Dates work too. I have a line I'm pleased with in the third book draft which says He died on the 15th of Hekatombeion. But in general, I'm working with modern, idiomatic English.
I'd love to hear how everyone else handles this.