Well - the free internationalization add-on will allow you to specify language specific content sections under pages called fr etc.. However, it doesn't as far as I am aware provide any language detection to switch the locale. For the most part, this isn't an issue, because you will need to provide your own content in the correct language for the pages under fr. But strings in packages and blocks would not be translated without switching the locale.
I need to test this actually... The locale really needs to switch to the content section you are in... I'm sure this could be achieved in the internationalization add-on.