If I am not wrong, the display of dates in french format is not supported on the leads dashboard :
It works perfectly in the deals's one :
Could you please have a look ?
Currently, the Leads inbox and Deals list view are set up a bit different indeed. Also in English the Leads one would state "Tomorrow" instead of a specific date for example. I understand the need for it to be aligned and surely something we can take into account for future updates.