There is an accessibility issue with Polylang in the menu. The current language is given only by CSS. Thus is a user doesn't have CSS (e.g. screen reader user), he miss the information.
The solution would be to add some markup (em or strong) on the current language.
All is fully described and testable here: http://blog.tanaguru.com/2013/11/27/internationalisation-multilingual-blog-and-accessibility-in-wordpress/#improvement-accessibility
I would be happy to help correct this issue