Miscellaneous topics that do not fit into specific categories.
Install the language accessory pack that you need. Go to https://support.microsoft.com/en-us/office/language-accessory-pack-for-microsoft-365-82ee1236-0f9a-45ee-9c72-05b026ee809f .
Note that doing this will start setup and it looks like you are installing Office from the start, but the process will be faster than if you really did start from scratch. When the install is completed, you will see an entry for "en-us" (if you installed the US English language pack, that is) alongside the "fr-fr" one.