Transifex doesn't have a locale for Ancient Greek defined, but I have found them very approachable, so I could request one for you. We will need to supply the plural form rules and the ISO language code.
This is what the plural form rules look like for Modern Greek: https://www.unicode.org/cldr/charts/latest/supplemental/language_plural_rules.html#el
This is what I have found for the ISO language code:
Greek, Ancient (to 1453)