the greek toponymes finished in -ista (not ishta) have latin roots, because of the occupation of 1204.This doesn't mean the natives have anything to do with

As far as I'm familiar with the Greek language the sound 'sh' is absent from the Greek phonology. It is usually simply replaced with 's'.

Anyway, exonymy doesn't apply on microtoponimy. Names of villages are usually given by the people founding and populating them.

I think you are very confused.I talked to you about what natives feel, not what language they speak.so would you like to tell me what they told you when you told them "you are not Greeks"? ;D

but still, even if we talk about language, you are talking about 100.000 people in a region of 2,5 millions

I do have some deep roots from the southern part of Kastoria perfecture, and visit Macedonia very often. The language you are talking about is mostly common in Florina and kilkis (in my perfecture only in the northern part in 2-3 villages), and as far as i know around 100.000 do either speak the language or have partially ancestry from speakers of the language.

I haven't been to Kostur/Kastoria region. I can't speak of the situation there. I only know there were settled some 10.000 refugees from Anatolia in that prefecture in the '20s, but I haven't made any more detailed research.

Also, I can tell you that almost every single individual in Republic of Macedonia (also in the diaspora) can trace some origin back to Aegean Macedonia. There is an ancestor in every family born somewhere there. This does not tells that much for a population migration, as it does for the contacts and the unity of the population in whole Macedonia.

The majority of speakers have learned the language either recently or (when we are talking about non Greek speakers) were forced to change their language during medieval times after occupations by slavic empires, but didn't lose their identity.

That's not logical.

You're implying that Greeks were forced to change their identity, so that you can justify your forceful assimilation as "back to the root" process.

Medieval states were not based on ethnic principles. The rulers didn't mind much for the language the peasants spoke as long as they were paying their taxes.

States created in modern age, however, are based on ethnicity turned into nationality; and it is important for the population to be homogeneous. This is why your theory about forceful assimilation of Greeks in the Middle Age is not plausible, in contrast to the forceful assimilation of the Macedonians in the Modern Age.