This is more or less possible. What is provided by B2evo is the default locale for the blog and the default locale for the member. So your members can choose their language and will see the headlines in your blog through the translation of their choice -provided you installed that translation-.

I think there are more solutions, so let's hope there are more reactions to this topic.

Good luck

Thanks Afwas for your comments.

I have a feeling that it could be doable relatively easily if we can pass some variable to ask the system to ignore the blog's default _global.php file.

There are at least three levels of _global.php exist, for individual blog, global, and system.

Currently, I think the blog's setting is stored in the database and its' the only source of direction for this setting. However, if the selected _global.php file is not found, the system automatically fells back to the system level (English) which coming from installation. It won't look back to the _global.php defined at the global level.

If the system will look up some variable at the first place, instead of the blog's setting, then it could enable this feature. The client's variable can be submitted as part of query string, or a cookie.

Yes I also doubt how practical this would be since on a blog, all categories, posts, and comments would be written in the language selected by the blog owner. If the visitor can't comprehend those contents, the menu in the understandable language will help little, though. ;-)

I will hold back this idea for now.