Multilingual website: problem with admin language

Hello,

In a multilingual website with 2 languages (EN, FR) managed by the Internationalization module, I added the Administration menu and Administration modules to managethe admin language of my website. Languages ​​are managed by folders in path :

FR: mywebsite.com/fr
EN: mywebsite.com/en

The problem is that in the admin language changes according to the language in frontoffice. And oddly it is the opposite:

FR in frontoffice : EN in admin
EN in frontoffice : FR in admin

Yet here admin/config/regional/language FR is checked in the "Admin" column
Here admin/config/regional/language/admin_language I enabled "Force use of default language" and "Use administration language in the administration menu"
Here admin/config/regional/language/configure, the method "URL" is selected and the first position

I tried to check / uncheck other options but anything change.

Have you any idea to have the admin in FR continually whatever the front page displayed?

Thank you

Phil