I have Windows 7, but not the French Version. Have no problem saving images. I right click, and choose save as, and can add where to locate it in my computer.
I recently added the Opera extension, Photo Tagger.
https://addons.opera.com/en/extensions/details/photo-tagger/?display=en
There if you click on the star (that will appear on images after you download and install the extension), you can instantly save the image to a folder in your speed dial. You can if you choose then open up that image, right click on it and save it in your computer. Perhaps, that work-around might at least solve the immediate problem, if you can save the image that way to your computer from the Photo Tagger display of your favorite images on your speed dial.
Still sounds like something is wrong with your Opera. Maybe a bug. It would help if others with Windows 8.1 (the French version) (or just Windows 8.1 in general) comment on whether they are having a similar problem. Bonne chance!