✅ Step-by-Step Guide to Add Categories in SharePoint Calendar
Go to Your Calendar List ( site contents - events)

Open the calendar list (classic or modern list depending on your setup).
add event (+add)


Under the Columns section, click on Category.
Create Categories: French and English

Save your changes.
Use Categories in Events:

Go back to page. Create events. Edit page. 
Edit Properties - Category - 
Select the appropriate category for each event. Filter or Display by Category per page
In the Events web part, you can choose to display events by selected categories 1.