Multiple inconsistencies when changing the default language of a page

To reproduce:

• Set the wiki as multilingual
• Edit a page
• Create a translated version of the page
• Modify the default language using the Document Information panel
• Switch between the translated versions multiple times and try to reedit or export the pages.

After changing the default language of a page the following errors appear:

• The menus are inconsistent with the translated version of the page(Eg: export as pdf will actually export the document in another language)
• Available document languages is broken(the new default language may appear twice)

It seems that Document.getRealLanguage() doesn't have the right value. This value is propagated in xwikivars.vm($languageparams, $docvariant ) and then to the to other templates.