Latest possible POD for German-speaking majority in Hungary before age of nationalism

What would be the latest possible POD to get a German-speaking majority in Hungary before the age of nationalism?
 
The problem is that the age of nationalism coincided with the rise of public education, which was a huge factor in language shift across Europe. Before you have universal public education, you have no easy way of peacefully getting people to stop speaking what they've always spoken.
 
The problem is that the age of nationalism coincided with the rise of public education, which was a huge factor in language shift across Europe. Before you have universal public education, you have no easy way of peacefully getting people to stop speaking what they've always spoken.

I was thinking of something like a much larger German immigration into Hungarian territories than in OTL, so the POD would probably have to be quite early. How long time would be needed in order to make a German-speaking majority with a larger, but realistic level of German immigration? And what made German-speakers settle in some Hungarian areas rather than others? I guess German majorities in the cities would be the best way to boost German-speaking majority in modern time.
 
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