The WordPress 3.9 update broke by blog, it took me some time to find the culprit: the qtranslate plugin. It was causing all sort of minor problems in the past, so I decided to just turn it off. I started using it at a time when I was using way more different languages in this blog, and I never managed to find a satisfying way to use it.
The underlying problem still remains: I write in this blog in multiple languages, something the Web in general and WordPress in particular have trouble coping with, simply trying to solve it in an add-on simply does not work. Internationalisation, like security and reliability are not something you can add as an afterthought.