Just saw this topic, so I am sorry it is such a late response. I hope you figured it out, but found something that would be useful for you:
I know a lot of sites will redirect a user to a subsection that corresponds to the language and the main domain shows the primary language you are targetting. Something like:
www.example.com <- content in primary language
www.example.com/en/ <- content in english
www.example.com/ru/ <- content in russian
www.example.com/sp/ <- content in spanish.
This would definitely be safer than showing different content on the same url based on some criteria.