"Byl to velmi nešťastný den."

Translation: It was a very unfortunate day.

[Jean290771]

jednou mi to neuznalo unhappy, ale chtělo to unlucky.
Když jsem dal unlucky, chtělo to unhappy.
Co s tím?

[Dmitry532061]

Why "unlucky" isn't accepted?

[VladaFu]

It is. Always report complete sentences, single words are not very useful.

[Tom260364]

a proč ne "sad"? ("sad day" is standard American English; "unhappy day" is OK sounds contrived to American ears)

[endless_sleeper]

'sad' = smutný

Nešťastný den nemusí být nutně smutný.

[Tom260364]

Díky. But in English, "a sad day" is not literally referring to emotion (a day of mourning) but to unfortunate events. E.g., "It was a sad day for the US when Donald Trump was elected president." That statement is separate from a statement about whether people were sad or happy; rather a commentary on a misfortune. So my sense is that "sad" is used here in the same sense as "nešťastný" in the Czech phrase.