Dialog box for saving file does accept non-ASCII character

When I ask to save a file, an error window pop-up at each time I enter the letter "é", saying that the name is invalid.
This is particularly annoying as the default name in my language (French) is "Document numérisé.pdf". Thus, an error box pop up each time I want to save a file.
The warning message comes from GTK+, not simple-scan. But I have other GTK application in which I can use "é" in file names.
Version : simple-scan-3.14.0-3.mga5
On Mageia 5.
lib64gtk+3_0-3.14.8
or
lib64gtk+2.0_0-2.24.26

The log file contains only the final file name.
The warning box has no title and says exactly : "Nom de fichier non valide" or when launched with LANGUAGE=C prefix: "Invalid file name"