Most Poles leave the house to go na dwór (i.e. ‘outside’ in Polish, but literally ‘into the courtyard’, though if someone has ‘gone out into the street’, it probably means to join a crowd of demonstrators). But residents of Kraków and the Lesser Poland region leave their homes to go na polu (‘into the field’), which is an endless source of arguments.
The proud inhabitants of Lesser Poland even came up with a meme: Nigdy nie przestanę wychodzić na pole! (‘I’ll never stop going out into the field!’), and a whole posse of Kraków rappers recorded a track titled Chodź na Pole (‘Let’s go out into the Field’). Many believe that the differing expressions arose from differences between cities and the countryside — Varsovians could have a dwór (which also means ‘estate/manor’ in Polish), while the humble peasants of southern Poland had to go out into the field. Moreover, the prominent linguist Jerzy Bralczyk stresses that the word dwór originally meant only a courtyard, not a lordly property.
So why did the Warsaw term become the norm, with the Lesser Polish version deemed a regionalism? Linguists explain it as follows:
The Polish language developed under the influence of each successive cultural centre and its surrounding dialects — initially Greater Polish, followed by Lesser Polish and, finally, Mazovian. After the First World War […] Poles speaking in different dialects were reunited in one country. […] Centralising the state encouraged the expansion of linguistic norms from the cultural and political centre. Therefore, ‘na dwór’ was regarded as standard, not a regionalism.
Using regionalisms is by no means a mark of illiteracy, although the form na dworzu is truly illiterate, since dwór is of masculine gender, so it should be na dworze.