[gtkada] problem with encoding

[jf Menon]

Hello, I use gtkada under a linux system (centos) that is localized with
fr_FR.utf8.
My application display text in a Gtk_Text. When the text is taken from a
file encoded in utf8, the display is bad in the gtk_text.
when I type directly into the widget, the display is bad too.
When I make a file encoded in iso88591, the display becomes good ! the
same result if I set the LANG=fr_FR.iso88591 and type from the keyboard :
the gtk_text display text ok.
It seems gtk (gtkada ?) "forces" translation from iso8859 to utf8
without warning ?
When I take the utf8 file, and use Glib.convert(text, "iso88591" ,
"utf8"), the display becomes good too. This behavior is very misterious
to me.
Using a gtk_entry to enter text into the gtk_text causes problems too
(the display is ok in the entry, but not when copied into the gtk_text !).
The problem is even worse with the windows version of my application
...("iso88591" does not work ...)

I am not experienced with l10n problems, it would be nice if someone
could give me a clear (short ?) way to handle the problem with GtkAda ?
Thanks,

jf