@olivier-rb ,
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Please go to File>Options>Language in Outlook to check and make sure the language setting is correst.
And then check if your Windows time zone and language are set to French.
If the above are correct, please close Outlook first.
Press Win + R, type Outlook.exe /resetfolders in Run box and press Enter to check this issue.
For more information: Folder names are incorrect or displayed in an incorrect language in Outlook.
Any updates, please let me know.
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