Now, last week an italian guy gave me some scripts to automatize the
building process (you still need to edit .ini and some .js files,
thought), so I think this is a big thing enough to report it here, since
it will save you a lot of time.
You can find the how-to I wrote here:
http://developer.mozilla.org/En/Creating_a_localized_Windows_installer_of_SeaMonkey
and I write about these scripts in the last paragraph. Try them if you
want, and ask me if you have some questions.
Speaking about scripts, I want to remember you that KaiRo has written
two bash scripts to make a localized Windows zip and Linux tar.gz
without efforts. You can find them here:
http://www.mozdev.org/source/browse/kairo/src/l10n/scripts/
bye,
Iacopo