Offline mode and streaks
I'm going on holiday for two weeks to a rather remote, internet-less Italian villa. Do lessons completed offline also sync a timestamp, so that I might have a chance of keeping my glorious 76-day streak?
I spent a week and a half using offline mode on my iPhone in the cloud forest of Mindo in Ecuador. It can be really wonky so be careful... for example: Sometimes the points don't sync correctly and you end up losing points, occasionally when you're syncing the app will stop using the network and you'll think the lessons are downloaded until you go to use the app offline and find that there are no lessons to enjoy, if you have a slow connection and you try to play through a lesson online occasionally the audio just doesn't download and you'll have to answer questions without it, if you fail the last lesson in a skill it will still mark itself as completed, etc.
To answer your question about the streak, I have a strong feeling that the answer is no because when I sync the app all of my completed lessons marked as having been completed on that day.
fyi: You'll need to resync after about ten lessons in order to download more. Sometimes the app will download more, sometimes less and there's no way to tell which lessons are downloaded until you take it offline so check before you leave your hotspot.
I recently went to Cancun for 6 days and had zero cell signal or wifi. I used Duolingo Plus and downloaded the offline lessons. I also used a Weekend Amulet because my flight arrived on a Saturday.
So, I didn't practice Saturday or Sunday. Then I used offline lessons for Mon, Tues, Wed, and Thurs. During that time, the app said I had lost my streak. However, when I arrived home Thursday evening, my streak was back and my Weekend Amulet had been consumed/used.
In summary, I was gone for 6 days, used offline lessons only, streak came back when I reconnected to wifi at home.