Duolingo is really a good software for languages learning.
Currently I am learning three languages in Duolingo, French (le français), German (Deutsch), and Spanish (español, castellano).
I have tried Italian (italiano) and Portuguese (português), but I have no time and effort left for these two.

At first couple months, I tried to go a full round everyday. I got a lot of experience points. However, the progress was not promising. Now, I change the strategy. Keep going advance everyday and try to finish three icons a day. If I can keep this pace, these three languages should be finished in six months. This pace is really hard to keep. I have little time besides paper and thesis writing. Not to mention that I have to practice and exercise everyday. I can only exercise duolingo in lunch time and in spare time with my smart phone.