Obviously Macedonian language listed by Hieronymus Megiser in 1603 was Slavonic, as you can see when reading that line.
So it's not the same language as that which existed in Ancient times. But this language has also been called Macedonian since at least 1603.
However - as was mentioned on the other thread - historical 'Macedonia' (now a province of Greece) and the modern state of Macedonia are not the same.
Historical province of Macedonia divides into 3 parts - Vardar, Aegean and Pirin (of which Vardar corresponds to modern state of Macedonia):
But despite the fact that modern state of Macedonia includes only Vardar, many of its citizens are descendants of people from Aegean.
Those Slavic-speaking Macedonians were deported from their native province of Aegean during the 1920s.
Although Aegean part belongs to Greece today, Greeks were not a majority in this region in 1913:
Total population of Aegean in 1913 - 1,052,227 - including:
Slavs - 370,371 (35,2%)
Turks - 274,052 (26,0%)
Greeks - 236,755 (22,5%)
Jews - 68,206 (6,5%)
Vlachs - 44,414 (4,2%)
This changed only as the result of post-1913 population movements (deportation of native local Slavs, immigration of Asian foreigners):
In total 130,010 native Macedonian Slavs were deported, while at the same time 618,199 Christian colonists from Asia Minor came.
Many of those foreign newcomers to Macedonia from Asia Minor did not even speak Greek, but Turkish or some funny local dialects:
They identified as "Greeks" only because they were Christians - not Muslims. But their language was in many cases not Greek:
http://en.wikipedia.org/wiki/Karamanlides
A CAMP SCHOOL FOR CHILDREN OF REFUGEES AT SALONIKI
The Anatloian "Greeks", exiles for many centuries from their native land, spoke a tongue different from that spoken by the Greek proper. Therefore the first duty of the Greek Government was to teach Anatolian "Greeks" to speak Greek.
There are also many people with Albanian ancestry among modern Greeks:
Attica used to be populated mostly by Albanian people around year 1830:
This is according to an English book published in 1855 (MDCCCLV):
From:
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The largest city of the Aegean region was also not Greek in 1913.
Population of the city of Salonica in 1913 was as follows:
In total - 157,889 inhabitants - including:
Jews - 61,439 (38,9%)
Turks - 45,867 (29,1%)
Greeks - 39,956 (25,3%)
Slavs - 10,627 (6,8%)
And it had been like that since at least around year 1500:
Proportion of Jews, Greeks and Turks:
https://upload.wikimedia.org/wikipedia/commons/d/db/Saloniki_population_graph.png