"We saw a waterfall while hiking."

Translation: On a vu une cascade en faisant de la randonnée.

[pemerita]

why not ' nous avons vu' rather than 'on a vu' ?

[Louradour5]

I guess it has not been marked wrong, we can say both.

[MandyB11]

Both are acceptable. Nous always means we, whereas on can mean we, you & (some)one. Context will tell you about the latter. But when you translate "we", use either one. Just remember to match the verb(s).

[LoisDelaney]

When is it preferrable to use "on" rather than "nous"

[--Roody--]

On is less formal than nous. Use on in everyday speech and casual writing.