NewJoker subsequently to excluding Windows from the change made in July, the root cause analysis has been done by @bdm concentrating on the issue from a French language angle. It boils down to the accents on calendar months so in your case Sierpień for August.
The fix https://github.com/FreeCAD/FreeCAD/pull/10403 changes the formatting of time and date. Even though the regression was introduced in July, neither the French nor Polish for July has an accent so it wasn’t instantly noticeable!! I’ve searched the entire codebase and it’s the only occurrence I can find for this scenario.
