This issue occurred on a C3. As there is a lot of commonality between Citroen models I have posted this here.
Whilst I understand that disconnecting a battery will cause reversions to kph, kilometers, loss of date and time, and reversion to French, I had an incidence today where I left home with everything OK, and when I got to my destination all of the menus and warnings had reverted to French. All of the other parameters were as normal. Not a big issue, but this was the second time it has happened, and I was wondering if anyone else has had this issue. The car is a 19 reg C3 110bhp Flair.
Faults and Technical chat for the Citroen C4 Cactus