It's very easy to change the language from English to French on the NP800 series relays, however, if the relay is set in French, and you don't speak French, it might not be so easy to change the relay back to English. The procedure for the NPI800 is:
  English Display   French Display  
Key Press Line1 Line2 Line1 Line2
Enter Main Menu Measurements Menu Principal Mesures
Up Main Menu Events Menu Principal Evenements
Up Main Menu Information Menu Principal Informations
Up Main Menu Change code Menu Principal Changement code
Up Main Menu Modbus Comms Menu Principal Communic. Modbus
Up Main Menu Operation Menu Principal Exploitation
Enter Language English Langue Francais
Right Language French Langue Anglais
Enter Password? #### Code d'acces ####
Enter Password? Password OK Code d'acces Code valide
  Reglase LCD 110 Adjust LCD 110
Clear Sauvegarde en attente...   Waiting to save...  
  Menu Principal Exploitation Main Menu
Clear Quitter le mode Parametrage? Quit settings Mode?
Enter Courant I1 0.0A Current I1 0.0A
If the default display has been changed from red-phase current, then the relay's display will differ from the final row of the table. 
For more information, see section 5.13 of the NPI/NPID800 user-guide, section 5.13 of the NPM800 user-guide, or section 5.10 of the NPU800 user-guide.