This page contains questions about courses (often referred to as "skill trees").
What's a language tree?
Main article: Language tree
The way Duolingo teaches requires users to finish a skill or set of skills before moving on to the next set . The skills are displayed in a way that makes them look slightly like a "language tree ". Users must complete all the skills on each row of the tree before moving to the next row.
Will I be fluent when I finish Duolingo?
Words you know, how important those words are, how well you know them, and how likely you are to forget them.
Why doesn't course X have bonus skills or words?
What is the recommended learning routine?
According to Duolingo, "learners should first focus on finishing all the lessons [of level 0] in a skill, and later come back to review them at just the right times". This means that if you are doing a tree with 100 skills you will finish your tree with only 100 crowns from a maximum of 500. There is another method, called the waterfall method in which you are doing lessons of all levels at the same time, in a specific order.
Is there a standardized language proficiency test?
Where are the grammar explanations (tips and notes)?
How many people have completed courses?
As of October 2013 more than 100,000 people have completed a course.
In which courses do students make the most progress?
According to Duolingo, students make more progress in courses that teach English.
When are typos accepted?
According to CEO Luis von Ahn:
We accept something as a typo if it is one letter off AND is not a valid word. So for example, we accept "te" as a typo for "the" but we don't accept "he" as one.
Do lessons focus more on Recognition or Recall ?
The exercises have a careful balance between maintaining user motivation and teaching effectively. According to Duolingo CEO Luis von Ahn:
The issue is that every time we try to give more recall exercises (where you translate from the language you know to the new language), people use the website less!
What are streaks?
Main article: Streak
Your streak is a measure of how consistently you use Duolingo. Your streak increases by one for each day you meet your goal and resets to zero when you miss a day unless you buy a streak freeze ahead of time.
Will the courses ever be expanded?
Yes, there are plans to expand the current courses. For now there are Bonus Skills that can add more content to a course.
Why aren't there human voices in all lessons? 
This is due to financial and technical reasons .
How do I change what course I'm taking?
See this discussion with several methods to switch between courses among them some quicker than the one described by the following (official) link.
- Here is the official link.
- From the Home tab , click the language portal-badge (flag icon).
- Choose the course you want from the "Learning Language" options.
- Click "Save changes".
Notes: Changing to a course with a different base language (e.g. English in the example image) will also change the Duolingo web interface to that language. However, your progress in the courses from the original language will not be deleted.
Where is the vocabulary section?
How do I reset or remove a course?
How do I report an error in an exercise?
You can report an error in an exercise using the "Report a Problem" button that appears below the exercise after you've entered your answer. Check the checkbox(es) next to the error(s) you wish to report and click "Submit". 
Why aren't serious errors in sentences fixed quickly?
A "large fraction of the user reports are erroneous" so it takes considerable time for contributors to find and correct mistakes. Problems with audio are generally a result of connectivity issues or audio generated by TTS engines.
Where can I get help on an exercise?
- If you are doing a lesson (as opposed to a practice), look for the "Tips & notes" (or Grammar explanations) button near the top right of the exercise area.
- Use the "Discuss sentence" button that appears below the exercise area, and see if your question has already been asked and answered there. If it hasn't, go ahead and ask.
Note: Do NOT use the Sentence Discussion area to report an error of translation (e.g. that a correct translation is not accepted) that you are reasonably sure about.
How can I help others learn my language?
You may answer questions in the discussion or sentence discussion section. When answering a question try to back up your answer with dictionary or grammar references.If there is no section for the language you want to help with visible in the discussion area you will have to change to a course teaching that language to see it. Instructions for doing so are available here.
Can I change the voice in the lessons ?
How effective is Duolingo at teaching a language?
One scientific study found that "a person with no knowledge of Spanish would need between 26 and 49 hours (or 34 hours on average) to cover the material for the first college semester of Spanish." Duolingo has also several positive reviews and awards for their teaching methods.
What dialect does Duolingo teach for language X ?
Why does the course for language X use the flag for country Y?
Should I learn multiple languages at the same time?
What are XP?
What is the highest level?
The highest you can reach in a language course is 25 and requires 30000 XP .
How can I see number of XP left until next level?
The profile page should have that information.
What does my level really mean?
It just means that you've accumulated a certain number of XP from doing lessons & practices. Some correlation has been found between XP and word "peeks" on the one hand and standardized language test results on the other but the correlation isn't perfect. The correlation may also change as Duolingo changes how much XP is awarded for each task.
- For which courses do students make the most progress. Duolingo blog. Retrieved 2016-08-30. http://web.archive.org/web/20160830191856/http://making.duolingo.com/for-which-courses-do-students-make-the-most-progress.
- Recognition vs Recall
- "IAm Luis von Ahn, co-founder and CEO of Duolingo. AMA.", http://www.reddit.com/r/duolingo/comments/230umo/iam_luis_von_ahn_cofounder_and_ceo_of_duolingo_ama/cgsd5au
- Why aren't there human voices for the lessons?
- "Is there some way that more serious problems with the Duo Website could be given priority?",https://www.duolingo.com/comment/2405172$comment_id=2420531
- [https://www.duolingo.com/comment/2405172 Is there some way that more serious problems with the Duo Website could be given priority?]
- "What would you want to see in a FAQ?", https://www.duolingo.com/comment/781395
- "How effective is Duolingo?", https://www.duolingo.com/effectiveness-study
- "Duolingo’s Data-Driven Approach to Education", http://blog.duolingo.com/post/41960192602/duolingos-data-driven-approach-to-education