OK so I tried it here. First visit to the site, in English. First thing I did, I go to the French icon and switch to French. Site is now in French, as expected. Go to registration, boom, I get a French question, as expected.
Here's where it gets tricky, I then proceed to switch back to English, go back through registration, and now I'm still asked the question in French because it's stored in session. This is not unexpected, whether it's desirable is another matter.
How exactly did you try it out?
* Arantor suspects what needs to be done is to have it detect whether or not it is the same language as currently in use and if not, refresh and fetch new question informatin.