Multilanguage CMS - solution for a clean, maintainable build?

I have three suggestions for Wordpress (not in your question, I know, but you tagged it) :

If you are willing to spend money on it, I can recommend the WPML plugin for Wordpress.

If not, there are two posibilities for WordPress:

• Use the Multi-Site-Feature from Wordpress > 3.0 (one Site per Language)
• qTranslate linked with qTranslate Meta. I use it, and it works realy good (But never tested with 12 languages).

You've got plenty of beautifull CMS out there, no need to create another one!

My recommendation goes to Drupal which is great for that, you can add every languages you want, you can have localized interfaces, localized content, a great translated navigation. Drupal is really designed to be used as a multilanguage tool.

You can have an overview of the localized version of the interface around here: http://localize.drupal.org/translate

If you are willing to go that way, take a look at the i18n module (short name for internationalization).

You can also find a bunch of ressources on the web.

Good luck in your quest.

If you didn't depend on your CMS being PHP for some reason, Plone (written in Python) would solve your multilanguage needs. (UI already translated to 40 + langauages, multilingual content management etc)