6867: warn on gtk translation missing

Merge the fix from trunk:
    Give a dev-oriented warning on console and pop up a UI
    warning dialog for the user, when an inconsistent
    translation configuration is detected between gramps and gtk
    (happens when a langpack is missing on Ubuntu systems, e.g.)

    git-svn-id: svn+ssh://svn.code.sf.net/p/gramps/code/trunk@22683 4ae1f11a-8b86-4847-b8af-ab372f36d1fd

svn: r22685

gramps/gui/grampsgui.py

@@ -253,9 +253,22 @@ class Gramps(object):
         from .viewmanager import ViewManager
         from gramps.cli.arghandler import ArgHandler
         from .tipofday import TipOfDay
+        from .dialog import WarningDialog
+        import gettext
 
         register_stock_icons()
 
+        if glocale.lang != 'C' and not gettext.find('gtk30'):
+            LOG.warn("GTK translations missing, GUI will be broken, especially for RTL languages!")
+            WarningDialog(
+               _("Gramps detected an incomplete GTK installation"),
+               _("""GTK translations for the current language (%s) are missing.
+<b>Gramps</b> will proceed nevertheless.
+The GUI will likely be broken as a result, especially for RTL languages!
+
+See the Gramps README documentation for installation prerequisites,
+typically located in /usr/share/doc/gramps.""") % glocale.lang)
+
         dbstate = DbState()
         self.vm = ViewManager(dbstate, config.get("interface.view-categories"))
         self.vm.init_interface()