"Kateřina chodí na vysokou školu."

[Shathu_Entayla]

Why is "Katerina is going to university" wrong?

[Hugo647250]

I would agree the indefinite article is not entirely necessary - I suppose maybe a semantic shading, going to a university as opposed to a college or a technical institute, for instance, would require the "a".

[Shathu_Entayla]

Actually, that depends: https://forum.wordreference.com/threads/im-going-to-university-to-the-university.3267656/