It is common in translation teams when a message does not need/require
translation to simply copy the "msgid" content to "msgstr". For example,

msgid "GConf"
msgstr "GConf"

This is quite common for the locales en_GB, en_CA where the vast
majority of the messages remain the same.

The problem arises from the fact that when compiling those PO files into
MO files (with "msgfmt"), the copied messages are included, contributing
to an increased size of the file on disk, and also in memory when the
application is loaded. The issue is, those copied messages could have
been ommited entirely in the MO file as the running application does not
need them (it can use the message text that is already included in the
executable).

The optimal solution is to fix msgfmt so that it omits those unneeded messages.

For a detailed description of the case see
http://blogs.gnome.org/simos/2007/07/23/important-mo-file-optimisation-for-en_-locales-and-partly-others/

I am not sure if the developers of gettext would be ok to change the default behaviour of msgfmt. If not (therefore, some extra parameter has to be specified), then the build system should accommodate for this parameter.

An alternative solution would be to assign the task to the distributions to optimise the MO files. In any case, this issue influences GNOME as a platform because less memory and disk space will be used, especially for the mobile platforms.

I think it would be good to keep this bug report on GNOME bugzilla to follow the case.