Date format French/Us english

Hi ! 

I have several Excel files ZIPed together.

All files have a French chart and and an English chart.
The French chart has bottom dates like " Juil -2019" and English ones like "Jul-2019".

But once  I receive the same ZIP, when I open the charts, all the English dates switch to French Format (because I guess I'm in France), but I want to keep the English date format on English charts.

I do not have time to go on each English chart, double clic on bottom date to change format, as I have about 30 to 60 charts to deal within 30 minutes.

Is there a solution to force Excel to keep the English date format ? 

This applies to Office 365 and Pack office 2010.

Thank you