Hello.
I don't know for the translation but I can try an explanation...
A bac blanc is a sort of repetition of the exam (baccalauréat) in order to train students before the real bac. This way they could feel more comfortable when the D-day will come.
That sounds like what we'd call a "Mock exam"... the format is the same as the real thing but the results don't count! It is like... a practice run, a rehearsal.
Tatz.
Therefore, a "Mock Baccalaureat Exam" or perhaps, a "Mock Bac"