"Learning Vietnamese needs diligence and patience."
Translation:Việc học tiếng Việt cần sự siêng năng và sự kiên nhẫn.
The course is not bad, but due to whatever reason they decided to skip the whole "vocabulary for beginners/elementary students" part and jump right to B1/B2-intermediate levels (or they just shuffled a ton of advanced vocab together with the basic words). That's why terrains/condolences/flexibilities are introduced before words such as remember/put/teach/wake up/rain and shop.
Still even these words are way better than infamous welders/snorkeling and toboganning you might find in ESL textbooks for kids (published by Cambridge, Oxford etc).
PS. It might be reasonable to finish another course in Vietnamese first which would target primarily beginners and then return to duolingo to review and expand.