Although it is ok to have some level of funny sentences, there are way too many of those in the Indonesian component of Duolingo. Having sentences that make sense is essential when learning a language especially since one of the most powerful learning experience comes when the learner actively comprehend and anticipate answers which is made impossible by non-sensical sentences. Furthermore, the vocabulary in general is quite redondant (how many sentences using "apple", really?) making it a poor learning experience after dozen of hours spent on the app. I understand that the contributors do it benevolently but that only underlines the shortcomings of the Duolingo business model: Wanting to make its design process as a "volunteer community effort" (i.e. free labour) while cashing-in profits from users like me that end-up paying good money for a lesser quality product using absurd, lazy and vocabular-deprived sentences.
Use your money to take a different course might be a better option. I started this course because it was advertised as free, unlike Babbel .. so I suppose I get what I am paying for. I don't now what the Babbel course is like.. might be worth a try? I do agree learning worthless phrases is silly, but as the others say, maybe because they're silly you remember more..