TerraDave said:
There are three ethnic groups, Magyars, the Romanians (called Vlachs, which I think is derogatory), and a third group, the “Saxons”, German speaking colonists brought in by the Hungarians (sometimes there is reference to another group of Hungarians, but here we are really getting into the details).
The second Hungarian group is called "szekelys" or "szeklers". They served as the guardians of the Hungarian borders and were thus free men - they had a collective nobility and didn't have to pay regular taxes. In the 1500s and 1600s, they remained Catholic when most of the other Hungarians, both in Transylvania and Hungary proper, turned Protestant.
The Saxons built the cities (which traditionally have both German and Romanian (and Hungarian??))names. The “vlachs” where not allowed in them.
Correct on the first. For example, Klausenburg is Kolozsvár in Hungarian and Cluj in Romanian. Much like Wien is Vienna in English and Bécs in Hungarian.
As for the second, I am not aware of that, although it is certain that settling in a city was not an easy thing in those days.
BEGIN EDIT There is of course also Gypsies!! END EDIT
Not in the old times. Horror movies seem to leave an impression that Transylvania is all about vampires and old, clairvoyant gypsy ladies. Neither were common until the 20th century.
The various ethnic divisions (4 main ones, plus outside intervention by Turks and Austrians) are one big source of conflict. This is compounded by religion, the Romanians are Orthodox, the Magyars Catholic. A Unite church was created to combine rights, but I don’t know much about this.
The united church is Unitarians or Anti-trinitarians (christians who don't acknowledge the Trinity). In the 16th and 17th century, Transylvania was probably the most tolerant country in Europe. In addition to the ruling Hungarian Calvinists, there were Lutherans (German city-dwellers), Catholics (Hungarian szekelys), Orthodox Christians (Wallachian and Moldavian shepherds), Jews and various fringe sects - Anabaptists, Unitarians and so on.
A good game oriented source is the Transylvania supplement produced for Ravenloft: Masque of the Red Death.
I wouldn't trust game oriented sources if you are going for any level of historical accuracy beyond "thar be vampires and gypsies, and they are all slavic!"