Language redirect based on browser's settings

Hello!

I have a website on Revo with three contexts.
I need a simple solution to redirect users only at the first visit.

For example, if the visitor has [en] in his browser, the website will redirect him to /en (and the same with /de for [de] and root for all other languages).
But if the visitor wants to see other contexts, my redirect shouldn't interfere him. And if the visitor leaves the website from /en version, but have [de] in the browser, the next visit should start from /en.

At the other time, what should we do with links from Google, leading to /en/about-company.html for [de] users? Should we redirect them to such page in Deutch or not. I have more questions than answers.

Hope for your help...