Finally this subject is solved!
I was using OX's repositories for Ubuntu server 10.04 (It is OX version 6.18.0.0-14). It seems that the package open-xchange-gui-lang-es-es is empty, it only has /usr/share/doc/open-xchange-gui-lang-es-es/changelog.Debian.gz and copyright files. Repository at http://software.open-xchange.com/OX6...untu10.04/all/

I search for a suitable package in Debian repositories at http://software.open-xchange.com/OX6...bianLenny/all/, I downloaded open-xchange-gui-lang-es-es_6.18.0.0-14_all.deb and installed it with dpkg -i. This package does have .js files at /var/www/ox6/3rdparty...etc.

Is this a bug in OX version for Ubuntu?
Will it be solved in the future so I can update packages via apt?

Thank you

PD: I've not been able to reply to the original thread. However, I think this information is important enough so I decided to post a new one. Sorry for the inconvenience!