What purpose do levels have?
Is it just a number, which represents my knowledge in a language? Or does it have more purposes?
It represents how much practice you have put into this language. If you earn 60xp, you go from level 1 to level 2. The higher up you go the more xp will be required to get to another level. So the first few levels are easiest to get. You can earn xp by doing the same lesson over and over or by doing different lessons or by doing translations in immersion. Here is a site which has a lot of information for new people, including a list of how many xp are needed per level. http://duolingo.wikia.com/wiki/XP http://duolingo.wikia.com/wiki/Getting_Started_Guide http://duolingo.wikia.com/wiki/Frequently_asked_questions/Courses
Yes, I rather challenge myself and not lose my streak. Some people like to gamble, because it makes them work harder. That does not work for me. I much prefer spending lingots to perhaps gain more or lose them, than to have my number of days in a row gone forever. You know what I would love to see is that when people go on vacation to the country whose language they were studying, that they would not lose their streaks for that but perhaps have it stop and pick up when they return.
Perhaps Duolingo could set up another counter that lists how many days they have been away and perhaps take away a lingot or so per day that they have been gone. I have seen people get so discouraged, because they lost their streak when they were the type of people who were practicing every day. If they really want to make people lose their streak for being away, they could set up a feature, in which you tell duolingo how long you will be gone for and if you don't come back then you could lose your streak. They could put a max time in. I think most vacations are a week or two, but some can be a month or some children go to visit relatives for the summer and it is not their fault that they don't have access.