Transfer "German from English" score to "German from French"
I am French and I was learning German from English because the German from French class was not offered at the time.
Is there a way to "transfer" my level from the "German from English" to the "German from French" class?
No, you can't do that explicitly.
But you could try to use your existing knowledge of German to test out of some of the skills, so that you can "jump up" the tree further. (I wouldn't recommend that, because the spaced repetition will make you revisit all the words eventually anyway - you're not saving yourself any work, just pushing it into the future.)
And in the forum, the level next to the German flag will sometimes show the highest level you have in one course, and sometimes a "virtual level" corresponding to all the XP you attained in all German courses.