I have tried to find this bug in the tracker, but I'have seen nothing like it.

To reproduce
1.log in as a teacher
2. click on "my courses" in the navigation block
3. click on one of your course
4.click on participants
5. click on "blogs"
6. the following message appears:
Coding error detected, it must be fixed by a programmer: Attempt to re-define already required string 'cancel' from lang file 'moodle'. Did you already ask for it with a different $a? Annuler !== Cancel