Let’s take the Greek State as 1832, when it had fixed boundaries.
I’m also going to use the pre-2010 Prefectures of Greece to break down the area of the new State.
We know that Arvanitika was spoken widely in the new Greek state. We know that many who fought in the War of Independence were monolingual Albanian speakers, who could not understand the instructions of Greek commanders.
15 of the 2010 prefectures were part of the new State. Of these:
- Arvanitika was the most widely spoken in Attica, Boeotia, Corinthia, and the Argolid, and the southern half of Euboea.
- As far as I know, it was all of Boeotia, most of Attica (Greek was limited to Athens, Aegina and Megara), most of Corinthia, and the eastern half of the Argolid.
- Arvanitika was a minority language in Messenia, Achaea, Arcadia, Laconia, and the Cyclades. Per Arvanitika – Wikipedia, not Elis.
- That leaves, by my guess, just 5 prefectures out of 15 where Arvanitika was not spoken: Phthiotis, Phocis, Eurytania, Aetolia & Acarnania, Elis.
Arvanitika and Greek were the major languages of the new State. I’m not aware of any Ladino: Jews in southern Greece spoke Greek. Not aware of any Slavonic spoken there since the Middle Ages. There would have been some Romany and Turkish spoken. There is a pocket of Aromanian spoken in Acarnania, per Aromanian language – Wikipedia.
I don’t have population numbers handy, and I don’t know if anyone does. Going by geography, Arvanitika was not the majority language, but it could easily have been spoken by a quarter of the population.