tangential: Regarding Duolingo, its nice that its a fun gamified thing for you and your wife to do together, consider formal education though. A 3-month class at community college will propel way further than believing Duolingo's method has short circuited a mental process. Duolingo is a decent addition to another learning method. But level 25 isn't going to be fundamentally different than level 7, it will never tell you "why/when/context" and that's very limiting, whereas a teacher can tell you in 20 seconds.