Does not work in combination with plone.app.multilingual 

If you combine webcouturier.dropdownmenu and plone.app.multilingual you would expect dropdownmenus in each LanguageRootFolder. But there is none.

Let us assume there are two languages 'de' and 'en'. in webcouturier.dropdownmenu.browser.dropdown is calculated a tabObj. 
A debug session gives the value: /plone/de/de/my-tab.
That is wrong. If you drop the second 'de' it works.

imo the tabPath should be calculated in the following way because in self.site_url is not taken into consideration that the Root is in the LanguageRootFolder.
```
tabPath = tabUrl.split(self.portal_state.navigation_root_url())[-1]
```
but not 
```
tabPath = tabUrl.split(self.site_url)[-1]
```