As described in this post:
http://devnet.kentico.com/Forums.aspx?forumid=46&threadid=21721
We have the same problem. We've added the key in web.config that you suggest but it seems doesn't make changes. The problem happen with IE9 and FF but not in Google Chrome. You can see the behaviour on this
link. The first time the language is switched but not the second or the other times.
Can you help us?
We have 5.5R2 license.