The link to the Menu Route Map is key.
I would expect those options to be "within" the scanner but accessible/configurable/selected via software hosted on the computer.
If ScanGear and CanoScan Toolbox - MP Navigator EX are not working then I do not know what to suggest.
The CanoScan Toolbox program appears (to me) to be the most promising because you do see the available controls even if they are in French. Is that correct?
Are you able to see the Menu Route Map (English version) that I referenced in my post (Post #2)? Multi-colored Menus that group related options.
Even if the preferences are all in French you may be able to use the Menu Route Map's context and format to identify the Language Option.
I used Google Translator to look up and translate Preferences, Display Settings, and Language from English to French.
The results:
Préférences Paramètres d'affichage Langue
Look for those words in French. If possible follow the menu route map from each word to the next.
Hopefully doing so will arrive at some list of languages where you can select English. In French = "Anglais"