It’s worth noting that the Ghost core team is working on internal projects that will make multi-language sites easier. The first stepping stone to this is the “Ghost's Channels - #8 by dsecareanu” project that would enable you to section your site via tag, that would open up the possibility of using #lang tags on posts to separate different languages.
There is also the “Nested/hierarchical tags, subtags - #2 by John” project that is in the pipeline that would allow more flexibility with language tags.
As the above two projects develop we also have plans for improving the UI and allowing customisation to better expose various “collections” of content. The idea being to make Ghost much more powerful and flexible, using tags and private tags to provide site structure.
So, while there is no specific multi-language support planned we’re definitely working on underlying improvements that will lead to multi-lingual sites being easier to work with.
In the meantime, the recommended approach is definitely to run a separate Ghost blog for each language and implementing some JS or very basic (even web-server level) server-side code for the redirects and/or cookies to remember a user’s selected language.