Why do I need to know plus ça change?
When you're sitting in a cafe in France with French friends the mood can turn pessimistic quite quickly and if it does then it's highly likely this expression will be used.
What does it mean?
Plus ça change literally means 'more it changes' which understandably won't make much sense to you if this is the first time you've come across it.
In fact, this is a very common way to shorten the longer expression plus ça change, plus c'est la même chose which means 'the more things change, the more they stay the same'.
And you may well have heard it said in English too.
In both languages the expression means the person who has used it is experiencing a certain kind of disillusionment or resignation.
For example it could be down to the fact that even though they have a new boss, the same old problems still exist in the team or that they have been visiting a psychologist but are still suffering from whatever it was that led them to book the appointments in the first place.
The expression is used on its own and is not considered to be slang.