Processes in Microsoft 365 for setting up Office apps, redeeming product keys, and activating licenses.
Which specific Microsoft Office product do you have? How did you try to add French? With recent versions (Microsoft 365, Office 2021, Office 2024), you would usually install a language accessory pack via https://support.microsoft.com/en-us/office/languages/language-accessory-pack-for-microsoft-365 .