You can perform "Windows System Assessment Scan" task on French OS managed client and check whether it applies to your imported updates or not, using "Compliance by Computer" report.
- Even if you have only "English" language enabled but there is a French OS client, there are updates with "Invariant Language (Invariant Country)" which should be available for localized OS patching.
As example of Software update with "Invariant Language (Invariant Country)"
If there will be updates without "Invariant Language (Invariant Country)", then you should include "French" language and perform PMImport to have required updates for French OS -> after that perform "Distribute updates" for further patching of French OS clients.
Thanks,
IP.