Fix l10n in Glade and Git plugins

The Glade plugin has some translations not being used, and the Git plugin has some string not being translated.

Some strings I kept out of this MR because I don't know if it is user-facing or some debug info, e.g.:

• src/plugins/git/daemon/ipc-git-change-monitor-impl.c:246

gerror:
  g_assert (ret != NULL || error != NULL);

  if (g_error_matches (error, GGIT_ERROR, GIT_ENOTFOUND))
    {
      g_dbus_method_invocation_return_dbus_error (invocation,
                                                  "org.freedesktop.DBus.Error.FileNotFound",
                                                  "No such file");
      return TRUE;
    }