I have xlsx files published in Sharepoint 2013. The date format of the regional configuration has been changed to Russian (Date format: DD.MM.YYYY).
After update file using the PowerPivot service Application, my slicers to filter data changed date format to american type (MM/DD/YYYY). And also the line of totals in the pivot table changes its name from Russian to English.
It's really important for me to solve this problem, I appreciate the collaboration.