The Nozatec devices I have came with French language already on them, if I ever wanted a different language it would have been just a matter of going into the settings to change it to whatever language I wanted.
Try deleting or renaming the folder named "Save", this will reset eveything back to default, then when it first starts up it should ask you what language you'd like to select, if your French language you've put there yourself is useable it'll show in the language settings, if it doesn't appear or is greyed out there's something wrong with it, the formatting or something & you'll need to source another file for the French language.
Deleting/renaming the Save folder might also help stop that error message, the program will create a new one auto when it's first run again.
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