correctly saved now, but...
Your suggestion solved at least part of the problem.
I changed the collation to "utf8_bin" of "table pg1_gallery_images" (screenshot369) and corrected the description of image 9 from the picture samples to "mon petit chien garçon". This time it was saved correctly in the database. (screenshot370).
But the text in the category manage images (admin/manageimages.php) is displayed incorrect still. (screenshot372). It now shows "mon petit chien gar�on."
The page encoding shows utf-8, though.
So, no joy yet...