Could this also be [formal] you did not speak enough, or must is start - O nem... [+ accent on O]
It can be both. And the way to differentiate is context. When you are formally talking to somebody, who just gave a speech, it is obviously the formal you. And if you are talking about a third person, then that's that.
"He didn't SAY enough" wasn't accepted. Should it?
It should not because "He didn't SAY enough" means "Nem SZÓLT eleget."
Or "nem mondott eleget"
What about this sentence puts it in the past tense?
The -t of beszélt.
In general, the sign of the past tense is -t-.
is elég a noun in this context? and that's why it has an accusative ending?
could you also say nem elég beszélt or is that different/wrong? Thanks!
Yes, you have to use the accusative ending -et. The form 'Nem elég beszélt' is wrong.
The contraction -- didn't -- was not accepted. Should it be?
(He didn't speak enough.)
Of course it should.