"Nós falamos sobre muitas coisas."

Translation: We talked about many things.

[bcouch]

How do we know it's past tense?

[Gaspard]

Can't tell out of context. Both should be correct.

[DanmacKinn1]

As "falamos de" is correctly translated in English as either "We speak of/about" and "We spoke of/about" either translations should be accepted. There is no way to tell past tense in this case with out a prompter such as ontem.

[roselaw]

It won't accept "of many things." Reporting it.

[DavidCheat1]

"Of shoes - and ships - and sealing wax-
Of cabbages- and Kings -
And why the sea is boiling hot -
And whether pigs have wings."