I have a confession. I kind of like Duolingo.
I've used it for years. It's a good tool, but it has its limits — it won't really help you learn a language by itself. Duolingo will help you assess your progress and whether you're improving, but it doesn't really give you the understanding you need to be even mildly competent in a language.
Recently, I was using Duolingo and a "translate this sentence" question popped up. It was something like: "Excuse me, can you give me my room key, please?" These typically trip me up, but I broke it down into the proper sentence pretty easily. In Japanese, a direct translation is something like: "Excuse me, room's key have please," or in Japanese, すみません、部屋の鍵ありますください。
I was feeling pretty cool for a couple days - it's a small win I know but I'll take it.
-Aaron