GtkBuilder uses GMarkup, which defines a boolean attribute as:
- yes/no
- true/false
- 1/0
The current ITS file used by xgettext to extract translatable strings
from GtkBuilder UI files only covers the first value.
See: 9e83eb65017cb38b809c733535195507bd442bd8
See: #4596
Recent gettext has a feature to allow consumer projects to supply their
own string extraction rules for XML files, in ITS format.
Gettext still ships the rule for *.ui, but it would be better
maintained in the upstream project.
https://bugzilla.gnome.org/show_bug.cgi?id=760202
