Some staff client UIs break with alternate default locale

EG 3.3

In eg_vhost.conf, there is a section under the heading "Run server-side XUL and XHTML through xmlent to load the correct XML entities" which uses en-US as the default locale for some parts of the client. If you use a different default locale, attempting to load some legacy UIs in the web client will result in an internal server error.

Apache logs show errors like the following:

unable to include "/opac/locale/${locale}/lang.dtd" in parsed file /openils/var/web/xul/server/admin/org_unit_settings.xhtml, subrequest returned 404

XMLENT XML Parse Error: syntax error at line 19: parsing /openils/var/web/xul/server/admin/org_unit_settings.xhtml: data [an error occurred while processing this directive]

The file opac/locale/en-US/lang.dtd exists, but any other installed locales do not include a lang.dtd file. There are other DTD files missing here too. I believe the issue was introduced by the fix for bug 1757455, which stopped copying these files into place for locales other than en-US.

Affected pages include Dojo-based UIs that still use old XUL/XHTML components. Under Administration > Local Administration:
 - Cash Reports
 - Shelving Locations Editor
 - Library Setting Editor
 - Non-Catalogued Types Editor
 - Statistical Categories Editor

Under Administration > Server Administration:
- Organizational Types
- Organizational Units
- Permission Groups

Administration > Reports also returns an internal server error.

Administration > User Permissions Editor appears to work as the interface opens with the patron barcode fields, but when you enter a barcode you get an internal server error.