Is it possible to sign up as a bilingual user?
I mean 'is it possible to signed up as a two languages user?' ... so I could choose to learn spanish from French, and to learn German from English. (french and english are my mothertongue(s))
You can add more than one course to take at a time. Here is how to do that: http://duolingo.wikia.com/wiki/Frequently_asked_questions#How_do_I_change_what_course_I.27m_taking.3F
However, only those courses that share a base language will be visible at a time. But, you can switch your view at any time by going into your language settings. :)