I agree, Openfire Server with Spark as the IM client will satisfy your requirements. It is a solid, extensible instant messaging server that should meet all your requirements.

What is nice about Openfire is that it allows you to centralize the management and security a lot, which gives you a lot of control in information-sensitive situations like this. It has integration with an existing LDAP/AD server if you want to keep your authentication policy centralized on your LDAP server if you have one. Likewise, you can force all users to use SSL for secure messaging if you want.

Likewise, I was working with the open source version over the last couple weeks (I setup a test environment for our company), and based on the menu options it appears that message auditing also is included (I didn't try it), so you can log all your conversations as you would like. I knew they had this feature before in their paid version, but it looks like they made it available in their open source version.

Finally, if you ever grow and need support, you can get it from their list of service providers. And it's free :-). It has easy installs for both Windows and Linux - definitely give it a try.
Good luck!

Openfire Server
Spark XMPP Client

I studied abroad in Quito, Ecuador for a semester while getting my Business Information Systems degree. I wasn't planning to take any CS/BIS courses while I was there, but ended up finding one that satisfied one of my major requirements. Anyways, it was a great experience and definitely worthwhile.

Since I've been out of school, I have learned that a lot of the countries that are strong in their IT outsourcing industry (India, Romania, Vietnam, etc.), have good academic programs specifically for CS. Sometimes, I wonder if some of these countries tend to prepare their college grads for the real IT world better than in the US (beyond just theoretical stuff). I don't know too many Spanish speaking ones, but you can try to do a little research to see which Spanish speaking countries are also strong with IT outsourcing. Just based on my very limited experience on the people/teams I have worked with, you can check Argentina, Chile, Bolivia, and of course Spain as a start.

Also to reiterate what other people have said here, when you go to study abroad, you are mainly going for the experience to immerse yourself in a new culture. So if you can fit some of your major requirements in, that's a bonus - otherwise, just try to work the study abroad experience in and get a chance to experience a new place/culture/language different from your own. In many ways, that in itself is a ton more valuable than anything you can learn in most of your courses anyways.

Buen suerte!