Add internationalization support to Middleman Blog. Thanks to that idea and realization:

https://github.com/onemanstartup/middleman-blog

You can use frontmatter or path's ":lang" part for language indication. Also you can use local_articles helper in templates to select only articles with selected language.
While creating article with rake you can pick a lang option now.
Tests are provided. I haven't much cucumber experience, but it seems, it works. Sorry, if I have a mistakes. Also sorry for my bad English very much.

Also in that squashed commit are small typo fix and fix of the unsafe moment for optional path's parts.