With German I have Level 8 and Crown Level 37. (7 and 21, respectively, with Spanish.) What, exactly, are these numbers telling me?
I think they are just there for motivation. I mean reading a book or watching a video in German/Spanish and understanding the content will tell you more about your level in both of these languages.
Not much more than how many points you have or how much repetition you've undertaken in a particular lesson. Duolingo levels have nothing much to do with your linguistic understanding.
The crowns are a reflection of how many skills you've completed, could be a mix of crown level ones, twos, threes and fives, depending. The level number simply reflects how many lessons you've completed. They tell you more about how much time you're spending on Duo than about how fluent you are.
they mean basically nothing :-)
8/25 levels (experience points = XP)
7/25 levels (experience points = XP)
The max crowns are max. skills x 5 + bonus-skills (only crown level L1)
You can find the max crown levels per tree on your SHOF progress page: http://www.duome.eu/Dan173745/progress
AS already said by others, the "crowns" the number of lessons (to be more accurate: lesson levels) you have completed. The "levels" are computed from so called "experience points", which roughly measure how much (in the sense of how often) you have been practicing.