Duolingo thoughts

Baseline core functionality for a language learning app:

• Complete grammar coverage. Grammar should be introduced slowly. For example, the old Spanish tree which threw the entirety of verb conjugation at you was frustrating, now it is introduced much more slowly and is much more effective.
• Ensure that each language teaches at least 4,000 words and the entire grammar space. I did some googling and there is definitely a range but a passive vocabulary from 3,000-5,000 words is necessary to be competent in said language up to about B2.
• Provide a guided learning experience. At the moment there are three vectors (lessons, levels and review) and it isn't clear what should be done, or in what order, or if it matters at all. Perhaps each person learns differently and they should experiment. If so, then tell us! On the flipside it should be able to watch over our shoulder and learn how we learn and customize the experience to each individual person.
• Language Practicing. Word and grammar decay. At the moment there is not a strong method for skill decay. Adding skill testing (rather than time based) embedded in the sentences could be used to implicitly test grammar behind the scenes.
• Progress reporting. I like the crown system with levels. Each level should be progressively harder, requiring more difficult and longer form interactions.

And a few tools:

• Grammar lessons with each section. I agree that you don't _need_ this as I am learning without lessons. But this can be very useful, and quite frankly speeds up learning, when you have a small amount of information available. An example of this is ser vs estoy, which I've had to look outside Duolingo to understand.
• Feedback on wrong answers. Showing the correct (and alternate answers) is good.
• A wordlist or dictionary to review your personal vocabulary.
• Add the ability to repeat skills or refresh. There are times when you run through a few lessons but you didn't really get it.
• "Test Out" checkpoints if you already have some proficiency in a language.

As of 6/3/2019:
Core functionality:

Tools: