Oh Sorry. In fact sudo needs absolute path with strace.
Funny things. By starting AppImage with
sudo strace -eopen -f my.AppImage 2>&1 | grep locale
Application is almost fully in french. In fact, starting application with sudo gives better translation (even if default gtk sentences are never translated). But with sudo, Gtk icons are missing (like in fedora in normal user: Error loading theme icon ‘image-missing’ for stock: Icon ‘image-missing’ not present in theme, … etc)
Strange !!!
$ sudo strace -eopen -f /home/lock/AppImage/Siril-0.9.4.glibc2.14-x86_64.AppImage 2>&1 | grep locale
[pid 5103] open("/usr/lib/locale/locale-archive", O_RDONLY|O_CLOEXEC) = 5
[pid 5094] open("/usr/lib/locale/locale-archive", O_RDONLY|O_CLOEXEC) = 4
[pid 5105] open("/usr/lib/locale/locale-archive", O_RDONLY|O_CLOEXEC) = 4
[pid 5108] open("/usr/lib/locale/locale-archive", O_RDONLY|O_CLOEXEC) = 4
[pid 5110] open("/usr/lib/locale/locale-archive", O_RDONLY|O_CLOEXEC) = 4
[pid 5119] open("/usr/lib/locale/locale-archive", O_RDONLY|O_CLOEXEC) = 4
[pid 5119] open("/usr/share/locale/locale.alias", O_RDONLY|O_CLOEXEC) = 4
[pid 5119] open("/usr/share/locale/fr_FR.UTF-8/LC_MESSAGES/coreutils.mo", O_RDONLY) = -1 ENOENT (No such file or directory)
[pid 5119] open("/usr/share/locale/fr_FR.utf8/LC_MESSAGES/coreutils.mo", O_RDONLY <unfinished ...>
[pid 5119] open("/usr/share/locale/fr_FR/LC_MESSAGES/coreutils.mo", O_RDONLY) = -1 ENOENT (No such file or directory)
[pid 5119] open("/usr/share/locale/fr.UTF-8/LC_MESSAGES/coreutils.mo", O_RDONLY <unfinished ...>
[pid 5119] open("/usr/share/locale/fr.utf8/LC_MESSAGES/coreutils.mo", O_RDONLY) = -1 ENOENT (No such file or directory)
[pid 5119] open("/usr/share/locale/fr/LC_MESSAGES/coreutils.mo", O_RDONLY) = 4
[pid 5118] open("/usr/lib/locale/locale-archive", O_RDONLY|O_CLOEXEC) = 5
[pid 5118] open("/usr/share/locale/locale.alias", O_RDONLY|O_CLOEXEC) = 5
[pid 5118] open("/usr/share/locale/fr_FR.UTF-8/LC_MESSAGES/findutils.mo", O_RDONLY) = -1 ENOENT (No such file or directory)
[pid 5118] open("/usr/share/locale/fr_FR.utf8/LC_MESSAGES/findutils.mo", O_RDONLY) = -1 ENOENT (No such file or directory)
[pid 5118] open("/usr/share/locale/fr_FR/LC_MESSAGES/findutils.mo", O_RDONLY) = -1 ENOENT (No such file or directory)
[pid 5118] open("/usr/share/locale/fr.UTF-8/LC_MESSAGES/findutils.mo", O_RDONLY) = -1 ENOENT (No such file or directory)
[pid 5118] open("/usr/share/locale/fr.utf8/LC_MESSAGES/findutils.mo", O_RDONLY) = -1 ENOENT (No such file or directory)
[pid 5118] open("/usr/share/locale/fr/LC_MESSAGES/findutils.mo", O_RDONLY) = 5
[pid 5120] open("/usr/lib/locale/locale-archive", O_RDONLY|O_CLOEXEC) = 4
[pid 5121] open("/usr/lib/locale/locale-archive", O_RDONLY|O_CLOEXEC) = 4
[pid 5124] open("/usr/lib/locale/locale-archive", O_RDONLY|O_CLOEXEC) = 4
[pid 5125] open("/usr/lib/locale/locale-archive", O_RDONLY|O_CLOEXEC) = 4
[pid 5132] open("/usr/lib/locale/locale-archive", O_RDONLY|O_CLOEXEC) = 4
[pid 5132] open("/usr/share/locale/locale.alias", O_RDONLY|O_CLOEXEC) = 4
[pid 5132] open("/usr/share/locale/fr_FR.UTF-8/LC_MESSAGES/zenity.mo", O_RDONLY) = -1 ENOENT (No such file or directory)
[pid 5132] open("/usr/share/locale/fr_FR.utf8/LC_MESSAGES/zenity.mo", O_RDONLY) = -1 ENOENT (No such file or directory)
[pid 5132] open("/usr/share/locale/fr_FR/LC_MESSAGES/zenity.mo", O_RDONLY) = -1 ENOENT (No such file or directory)
[pid 5132] open("/usr/share/locale/fr.UTF-8/LC_MESSAGES/zenity.mo", O_RDONLY) = -1 ENOENT (No such file or directory)
[pid 5132] open("/usr/share/locale/fr.utf8/LC_MESSAGES/zenity.mo", O_RDONLY) = -1 ENOENT (No such file or directory)
[pid 5132] open("/usr/share/locale/fr/LC_MESSAGES/zenity.mo", O_RDONLY) = 4
[pid 5132] open("/usr/share/locale/fr_FR.UTF-8/LC_MESSAGES/gtk30.mo", O_RDONLY) = -1 ENOENT (No such file or directory)
[pid 5132] open("/usr/share/locale/fr_FR.utf8/LC_MESSAGES/gtk30.mo", O_RDONLY) = -1 ENOENT (No such file or directory)
[pid 5132] open("/usr/share/locale/fr_FR/LC_MESSAGES/gtk30.mo", O_RDONLY) = -1 ENOENT (No such file or directory)
[pid 5132] open("/usr/share/locale/fr.UTF-8/LC_MESSAGES/gtk30.mo", O_RDONLY) = -1 ENOENT (No such file or directory)
[pid 5132] open("/usr/share/locale/fr.utf8/LC_MESSAGES/gtk30.mo", O_RDONLY) = -1 ENOENT (No such file or directory)
[pid 5132] open("/usr/share/locale/fr/LC_MESSAGES/gtk30.mo", O_RDONLY) = 4
[pid 5132] open("/usr/share/locale/fr_FR.UTF-8/LC_MESSAGES/libc.mo", O_RDONLY) = -1 ENOENT (No such file or directory)
[pid 5132] open("/usr/share/locale/fr_FR.utf8/LC_MESSAGES/libc.mo", O_RDONLY) = -1 ENOENT (No such file or directory)
[pid 5132] open("/usr/share/locale/fr_FR/LC_MESSAGES/libc.mo", O_RDONLY) = -1 ENOENT (No such file or directory)
[pid 5132] open("/usr/share/locale/fr.UTF-8/LC_MESSAGES/libc.mo", O_RDONLY) = -1 ENOENT (No such file or directory)
[pid 5132] open("/usr/share/locale/fr.utf8/LC_MESSAGES/libc.mo", O_RDONLY) = -1 ENOENT (No such file or directory)
[pid 5132] open("/usr/share/locale/fr/LC_MESSAGES/libc.mo", O_RDONLY) = 4
[pid 5132] open("/usr/share/locale/fr_FR.UTF-8/LC_MESSAGES/gtk30-properties.mo", O_RDONLY) = -1 ENOENT (No such file or directory)
[pid 5132] open("/usr/share/locale/fr_FR.utf8/LC_MESSAGES/gtk30-properties.mo", O_RDONLY) = -1 ENOENT (No such file or directory)
[pid 5132] open("/usr/share/locale/fr_FR/LC_MESSAGES/gtk30-properties.mo", O_RDONLY) = -1 ENOENT (No such file or directory)
[pid 5132] open("/usr/share/locale/fr.UTF-8/LC_MESSAGES/gtk30-properties.mo", O_RDONLY) = -1 ENOENT (No such file or directory)
[pid 5132] open("/usr/share/locale/fr.utf8/LC_MESSAGES/gtk30-properties.mo", O_RDONLY) = -1 ENOENT (No such file or directory)
[pid 5132] open("/usr/share/locale/fr/LC_MESSAGES/gtk30-properties.mo", O_RDONLY) = 4
[pid 5132] open("/usr/share/locale/fr_FR.UTF-8/LC_MESSAGES/atk10.mo", O_RDONLY) = -1 ENOENT (No such file or directory)
[pid 5132] open("/usr/share/locale/fr_FR.utf8/LC_MESSAGES/atk10.mo", O_RDONLY) = -1 ENOENT (No such file or directory)
[pid 5132] open("/usr/share/locale/fr_FR/LC_MESSAGES/atk10.mo", O_RDONLY) = -1 ENOENT (No such file or directory)
[pid 5132] open("/usr/share/locale/fr.UTF-8/LC_MESSAGES/atk10.mo", O_RDONLY) = -1 ENOENT (No such file or directory)
[pid 5132] open("/usr/share/locale/fr.utf8/LC_MESSAGES/atk10.mo", O_RDONLY) = -1 ENOENT (No such file or directory)
[pid 5132] open("/usr/share/locale/fr/LC_MESSAGES/atk10.mo", O_RDONLY) = 6
[pid 5132] open("/usr/share/locale/fr_FR.UTF-8/LC_MESSAGES/glib20.mo", O_RDONLY) = -1 ENOENT (No such file or directory)
[pid 5132] open("/usr/share/locale/fr_FR.utf8/LC_MESSAGES/glib20.mo", O_RDONLY) = -1 ENOENT (No such file or directory)
[pid 5132] open("/usr/share/locale/fr_FR/LC_MESSAGES/glib20.mo", O_RDONLY) = -1 ENOENT (No such file or directory)
[pid 5132] open("/usr/share/locale/fr.UTF-8/LC_MESSAGES/glib20.mo", O_RDONLY) = -1 ENOENT (No such file or directory)
[pid 5132] open("/usr/share/locale/fr.utf8/LC_MESSAGES/glib20.mo", O_RDONLY) = -1 ENOENT (No such file or directory)
[pid 5132] open("/usr/share/locale/fr/LC_MESSAGES/glib20.mo", O_RDONLY) = 8
[pid 5132] open("/usr/share/X11/locale/locale.alias", O_RDONLY) = 8
[pid 5132] open("/usr/share/X11/locale/locale.alias", O_RDONLY) = 8
[pid 5132] open("/usr/share/X11/locale/locale.dir", O_RDONLY) = 8
[pid 5132] open("/usr/share/X11/locale/en_US.UTF-8/XLC_LOCALE", O_RDONLY) = 8
[pid 5132] open("/usr/share/locale/locale.alias", O_RDONLY) = 8
[pid 5094] open("/usr/share/locale/locale.alias", O_RDONLY|O_CLOEXEC) = 4
[pid 5094] open("/usr/share/locale/fr_FR.UTF-8/LC_MESSAGES/bash.mo", O_RDONLY) = -1 ENOENT (No such file or directory)
[pid 5094] open("/usr/share/locale/fr_FR.utf8/LC_MESSAGES/bash.mo", O_RDONLY) = -1 ENOENT (No such file or directory)
[pid 5094] open("/usr/share/locale/fr_FR/LC_MESSAGES/bash.mo", O_RDONLY) = -1 ENOENT (No such file or directory)
[pid 5094] open("/usr/share/locale/fr.UTF-8/LC_MESSAGES/bash.mo", O_RDONLY) = -1 ENOENT (No such file or directory)
[pid 5094] open("/usr/share/locale/fr.utf8/LC_MESSAGES/bash.mo", O_RDONLY) = -1 ENOENT (No such file or directory)
[pid 5094] open("/usr/share/locale/fr/LC_MESSAGES/bash.mo", O_RDONLY) = 4
[pid 5094] open("/usr/share/locale/fr_FR.UTF-8/LC_MESSAGES/libc.mo", O_RDONLY) = -1 ENOENT (No such file or directory)
[pid 5094] open("/usr/share/locale/fr_FR.utf8/LC_MESSAGES/libc.mo", O_RDONLY) = -1 ENOENT (No such file or directory)
[pid 5094] open("/usr/share/locale/fr_FR/LC_MESSAGES/libc.mo", O_RDONLY) = -1 ENOENT (No such file or directory)
[pid 5094] open("/usr/share/locale/fr.UTF-8/LC_MESSAGES/libc.mo", O_RDONLY) = -1 ENOENT (No such file or directory)
[pid 5094] open("/usr/share/locale/fr.utf8/LC_MESSAGES/libc.mo", O_RDONLY) = -1 ENOENT (No such file or directory)
[pid 5094] open("/usr/share/locale/fr/LC_MESSAGES/libc.mo", O_RDONLY) = 4
[pid 5094] open("/usr/lib/locale/locale-archive", O_RDONLY|O_CLOEXEC) = 5
[pid 5094] open("/usr/share/locale/locale.alias", O_RDONLY|O_CLOEXEC) = 5
[pid 5094] open("/tmp/.mount_Z4BlPO/usr/././/share/locale/fr_FR.UTF-8/LC_MESSAGES/siril.mo", O_RDONLY) = -1 ENOENT (No such file or directory)
[pid 5094] open("/tmp/.mount_Z4BlPO/usr/././/share/locale/fr_FR.utf8/LC_MESSAGES/siril.mo", O_RDONLY) = -1 ENOENT (No such file or directory)
[pid 5094] open("/tmp/.mount_Z4BlPO/usr/././/share/locale/fr_FR/LC_MESSAGES/siril.mo", O_RDONLY) = -1 ENOENT (No such file or directory)
[pid 5094] open("/tmp/.mount_Z4BlPO/usr/././/share/locale/fr.UTF-8/LC_MESSAGES/siril.mo", O_RDONLY) = -1 ENOENT (No such file or directory)
[pid 5094] open("/tmp/.mount_Z4BlPO/usr/././/share/locale/fr.utf8/LC_MESSAGES/siril.mo", O_RDONLY) = -1 ENOENT (No such file or directory)
[pid 5094] open("/tmp/.mount_Z4BlPO/usr/././/share/locale/fr/LC_MESSAGES/siril.mo", O_RDONLY) = 5
[pid 5094] open("/tmp/.mount_Z4BlPO/usr/././/share/locale/fr_FR.UTF-8/LC_MESSAGES/gtk30.mo", O_RDONLY) = -1 ENOENT (No such file or directory)
[pid 5094] open("/tmp/.mount_Z4BlPO/usr/././/share/locale/fr_FR.utf8/LC_MESSAGES/gtk30.mo", O_RDONLY) = -1 ENOENT (No such file or directory)
[pid 5094] open("/tmp/.mount_Z4BlPO/usr/././/share/locale/fr_FR/LC_MESSAGES/gtk30.mo", O_RDONLY) = -1 ENOENT (No such file or directory)
[pid 5094] open("/tmp/.mount_Z4BlPO/usr/././/share/locale/fr.UTF-8/LC_MESSAGES/gtk30.mo", O_RDONLY) = -1 ENOENT (No such file or directory)
[pid 5094] open("/tmp/.mount_Z4BlPO/usr/././/share/locale/fr.utf8/LC_MESSAGES/gtk30.mo", O_RDONLY) = -1 ENOENT (No such file or directory)
[pid 5094] open("/tmp/.mount_Z4BlPO/usr/././/share/locale/fr/LC_MESSAGES/gtk30.mo", O_RDONLY) = -1 ENOENT (No such file or directory)
[pid 5094] open("/usr/share/locale/fr_FR.UTF-8/LC_MESSAGES/libc.mo", O_RDONLY) = -1 ENOENT (No such file or directory)
[pid 5094] open("/usr/share/locale/fr_FR.utf8/LC_MESSAGES/libc.mo", O_RDONLY) = -1 ENOENT (No such file or directory)
[pid 5094] open("/usr/share/locale/fr_FR/LC_MESSAGES/libc.mo", O_RDONLY) = -1 ENOENT (No such file or directory)
[pid 5094] open("/usr/share/locale/fr.UTF-8/LC_MESSAGES/libc.mo", O_RDONLY) = -1 ENOENT (No such file or directory)
[pid 5094] open("/usr/share/locale/fr.utf8/LC_MESSAGES/libc.mo", O_RDONLY) = -1 ENOENT (No such file or directory)
[pid 5094] open("/usr/share/locale/fr/LC_MESSAGES/libc.mo", O_RDONLY) = 5
[pid 5094] open("/tmp/.mount_Z4BlPO/usr/././/share/locale/fr_FR.UTF-8/LC_MESSAGES/gtk30-properties.mo", O_RDONLY) = -1 ENOENT (No such file or directory)
[pid 5094] open("/tmp/.mount_Z4BlPO/usr/././/share/locale/fr_FR.utf8/LC_MESSAGES/gtk30-properties.mo", O_RDONLY) = -1 ENOENT (No such file or directory)
[pid 5094] open("/tmp/.mount_Z4BlPO/usr/././/share/locale/fr_FR/LC_MESSAGES/gtk30-properties.mo", O_RDONLY) = -1 ENOENT (No such file or directory)
[pid 5094] open("/tmp/.mount_Z4BlPO/usr/././/share/locale/fr.UTF-8/LC_MESSAGES/gtk30-properties.mo", O_RDONLY) = -1 ENOENT (No such file or directory)
[pid 5094] open("/tmp/.mount_Z4BlPO/usr/././/share/locale/fr.utf8/LC_MESSAGES/gtk30-properties.mo", O_RDONLY) = -1 ENOENT (No such file or directory)
[pid 5094] open("/tmp/.mount_Z4BlPO/usr/././/share/locale/fr/LC_MESSAGES/gtk30-properties.mo", O_RDONLY) = -1 ENOENT (No such file or directory)
[pid 5094] open("/tmp/.mount_Z4BlPO/usr/././/share/locale/fr_FR.UTF-8/LC_MESSAGES/atk10.mo", O_RDONLY) = -1 ENOENT (No such file or directory)
[pid 5094] open("/tmp/.mount_Z4BlPO/usr/././/share/locale/fr_FR.utf8/LC_MESSAGES/atk10.mo", O_RDONLY) = -1 ENOENT (No such file or directory)
[pid 5094] open("/tmp/.mount_Z4BlPO/usr/././/share/locale/fr_FR/LC_MESSAGES/atk10.mo", O_RDONLY) = -1 ENOENT (No such file or directory)
[pid 5094] open("/tmp/.mount_Z4BlPO/usr/././/share/locale/fr.UTF-8/LC_MESSAGES/atk10.mo", O_RDONLY) = -1 ENOENT (No such file or directory)
[pid 5094] open("/tmp/.mount_Z4BlPO/usr/././/share/locale/fr.utf8/LC_MESSAGES/atk10.mo", O_RDONLY) = -1 ENOENT (No such file or directory)
[pid 5094] open("/tmp/.mount_Z4BlPO/usr/././/share/locale/fr/LC_MESSAGES/atk10.mo", O_RDONLY) = -1 ENOENT (No such file or directory)
[pid 5094] open("/usr/share/locale/fr_FR.UTF-8/LC_MESSAGES/glib20.mo", O_RDONLY) = -1 ENOENT (No such file or directory)
[pid 5094] open("/usr/share/locale/fr_FR.utf8/LC_MESSAGES/glib20.mo", O_RDONLY) = -1 ENOENT (No such file or directory)
[pid 5094] open("/usr/share/locale/fr_FR/LC_MESSAGES/glib20.mo", O_RDONLY) = -1 ENOENT (No such file or directory)
[pid 5094] open("/usr/share/locale/fr.UTF-8/LC_MESSAGES/glib20.mo", O_RDONLY) = -1 ENOENT (No such file or directory)
[pid 5094] open("/usr/share/locale/fr.utf8/LC_MESSAGES/glib20.mo", O_RDONLY) = -1 ENOENT (No such file or directory)
[pid 5094] open("/usr/share/locale/fr/LC_MESSAGES/glib20.mo", O_RDONLY) = 9
[pid 5094] open("/usr/share/X11/locale/locale.alias", O_RDONLY) = 9
[pid 5094] open("/usr/share/X11/locale/locale.alias", O_RDONLY) = 9
[pid 5094] open("/usr/share/X11/locale/locale.dir", O_RDONLY) = 9
[pid 5094] open("/usr/share/X11/locale/en_US.UTF-8/XLC_LOCALE", O_RDONLY) = 9
[pid 5094] open("/usr/share/locale/locale.alias", O_RDONLY <unfinished ...>