"Matěj has many sisters."

Translation: Matěj má mnoho sester.

[snikta]

not sure if I understand why it is sester not sestry - is it irregular?

[endless_sleeper]

'Sester' is genitive plural.

[tenpenny2]

Wouldn't it be accusative?

[VladaFu]

Not, mnoho and similar words require genitive.

[tenpenny2]

Oh yes, "of" many.....I forgot....Thanks. And, without a number of items, would it be accusative????