"Has he accepted that?"
Translation:Hat er das akzeptiert?
One is a third person singular pronoun, the other is a demonstrative pronoun.
You can use them in the same contexts frequently, but it changes a bit of the meaning and alters things like emphasis and tone in both English and German.
You can frequently find sentences that have approximately the same basic meaning as each other, but that doesn't make a direct translation of one of them into a direct translation of the other, and Duolingo prefers translations to be as close as possible.
I take your point.
But DL, which I love, is not perfect, sometimes it is inconsistent.
I think the German tree, is less inconsistent than, say, the English tree from Portuguese, where this, that, it, are often interchangeable, but not always.
I should also keep in mind the literal, rather than allusional, nature of German thought.
If you look at this website: http://www.vocabulix.com/conjugation3/akzeptieren.html you can see that "akzeptieren" is used in the future and conditional tense, not the past.