You will find the instructions for changing the language on the GPS in the Operating Instructions Manual.
I can only think you do not have the manual. You can download one free here:https://www.manualslib.com/manual/360975/Panasonic-Strada-Cn-Nvd905u.html#manual
Note: You will need Adobe Acrobat Reader software free.
When you download the manual and save it to your Documents folder, be sure to give the downloaded file a file name you can find again easily - maybe: Panasonic Strada CN-NVD905U.
The instructions for changing the language are on Page 19 of the manual.