Polylang support

Using a language plugin like Polylang it is possible to offer a site in multiple languages.
It would be nice if the Preferred Languages plugin allows specifying language preferences by active site language. E.g. when the user selects German (formal) site language (using Polylang language picker), the Prefered Languages plugin should first try German (formal) (de_DE_Formal) and then fall back to German non-formal (de_DE) (for which plugins are much more often translated first).