Translation:He forgot there was an important meeting today.
"He forgot there is an important meeting today" should be "He forgot there was an important meeting today", because of the sequence of the tenses. Reported on Nov. 19, 2017.
It's possible that the meeting hasn't taken place yet but the forgetting is in the past: "Do you know where John is? Don't tell me he forgot that there's an important meeting today!"
True, though even in that scenario it's still common in English to put the second verb in the past tense, as with reported speech. I.e. both versions are possible if the meeting hasn't yet taken place.
Both should be accepted.
We would need to know if the comment takes place before or after the important meeting to be able to determine whether "is… today" or "was… today" is most appropriate verb tense.
The Chinese sentence is ambiguous in this regard, and we are lacking additional context to make this determination.
Well he may not have missed the meeting yet, e.g. he went into work forgetting that he had a meeting later in the day and had to be reminded of it. This sentence still reads a bit wierd though, inserting a "that" makes it read better. "He forgot that there is an important meeting today.,"
There is no indication that the meeting was finished, so the sentence may not have been incorrect
How about "He forgot that he had an important meeting today"? That's what I wrote but it was rejected.
What about "He forgot today's important meeting" and "He forgot the important meeting today"?