"I know, I forget."

Translation: Saya tahu, saya lupa.

[Appers6]

When you load up Duolingo after skipping a few days...

[FresnoVegas]

Why is "aku" unacceptable here?

[Handrisuselo]

It should be acceptable. Maybe the participants (who contributed to translate Indonesian lessons) rarely used it, so the word "aku" was not saved in the Duolingo database.

I mean there is no the alternate translation "aku" in the database.

[lilohandaru]

Aku is the less formal word for I or me

[Serador2]

Aku tahu, aku lupa - should be accepted

[Twodu2]

In formal situations don't use aku, use saya

[ElinorGaul]

The story of my life............

[wanderdugg]

The english sentence should use a semicolon, not a comma.