Dropdown for language with post-filter

[JLKM]

Awesome theme this one with really advanced navigation. It worked right out of the box with no errors. It even swallowed my danish language file. Drop me a note, if I should add it to the project.

A few requests, though:

1. In my case the default.yml-language turns up on the site. How do I control the language in use.
2. Would it be too much trouble to add a dropdown language for the user?
3. And next: How about letting the chosen language filter out posts written in other languages?

These features are asked for everywhere. But I haven't found an answer to this request. At least not one, that works!