The language manager works like e.g. in Wikipedia. When you change the browser language, it does not react to that. The pages stays in the certain language. This is in Confluence an intended feature.
On the other hand, our solution Linchpin offers complete personalization:
That could solve your request. Using that feature, we solve this request in Confluence. According the profile information or settings, content is showed that is relevant to the user. And here also only in the language that the user speaks.