Translation:We pack our suitcases before our departure.
Most Americans, I believe, would not say "before our departure"; they would say "before we leave."
You are certainly right. However "before we leave" back translates to "avant que nous ne partions" (with a subjunctive and an expletive "ne").
The word taught here is "le départ".
While I agree "before we leave" is a bit more common "before our departure" doesn't sound out of place at all.
"We pack our cases before our departure" failed. Perfectly valid English form of the sentence.
saying "we pack", meaning present tense, when you're talking about something that seems to be in passed tense, sounds pretty odd. I mean...even in french that seems odd at least to me.
Duolingo marked "We pack our suitcases before we leave" as wrong, but that correction overlooks a fundamental difference between French and English: French more frequently uses a nominal style (favoring nouns over verbs). The phrase "before our departure" is perfectly correct, but more formal, in English, than the everyday "before we leave" (or "before we go"). I agree with Carl549388, and Sitesurf, but it is also important to point out the underlying principle.
What do you mean by more formal?
You seem to be an advanced student. Keep in mind that most of us are still learning basic vocabulary words. It's smarter for us to stick with the actual vocabulary words that we are being taught. You are more on the doctoral level, while I'm struggling with pre-K. Have you tried the language forums on sites like WordReference? You could have a great discussion there!