How does Duolingo determine my fluency?
It says I am 20% fluent in Spanish. How does that determine my fluency?
Duolingo is just throwing math at you, the consensus opinion seems to be that the percentage doesn't really mean anything.
Don't put too much faith in the number. Going through your tree (and reverse Spanish to English) will help, but will not make you truly fluent. DL is just one of your many tools - and it's a fun one! :)