If you are working on multiple languages, do you have to practice them all every day to keep your streak going?
Check out this wiki entry on how Streak and Streak Freeze work: http://duolingo.wikia.com/wiki/Frequently_asked_questions#How_do_Streak_and_Streak_Freeze_work.3F
I hope that helps! If you have anymore questions about Streak and Streak Freeze, feel free to ask! ^_^