UPDATE : As said in the WPML Forum, I had this issue only because the WPML plugin was not up to date on that website, there is no issue woth the latest version of Translation-management.
Hi ceralim,
It looks like you are using WPML, I had the same issue and found a fix by commenting a line in a JS file.
You can find my answer in WPML forum : https://wpml.org/forums/topic/bug-wpml-translation-management-when-i-updated-to-wordpress-4-5/#post-865098
