Try harder to look up the right localization

Try harder to look up the right localization

The code for looking up localized strings for action descriptions
was manually trying to break locale names into pieces, but didn't
get it right for e.g. zh_CN.utf-8. Instead, use the GLib function
g_get_locale_variants(), which handles this (and more). This fixes
the translation problem reported in
https://bugzilla.gnome.org/show_bug.cgi?id=665497

Signed-off-by: David Zeuthen <zeuthen@gmail.com>