Found a bug
I had two tabs open in my browser (firefox), one showing my own profile, another showing the french skill tree. I entered the immersion section and translated a few sentences of an article, excited and changed to my German tree. I returned to my computer a few minutes later, and entered the immersion-section again, but this time by clicking on the article I had just translated in the stream on my profile. I translated a few more sentences, and then returned to my profile where is noticed that the xp I had earned had been counted as German-xp not French-xp. I looked up at the flag next to my profile-picture and I noticed that the flag was still German. Summary: if you do stuff in the immersion-section the xp will be counted towards the language which flag is next to your profile picture, not the language which you are immersing in. If I should have written this post in another section please let me know, and I will send it where it needs to go.