Frank, thanks for setting up this group. From my conversations with other Jive customers both at Jive events and online, I think this is a really needed area.
I thought I'd quickly introduce myself for any future group joiners whom I haven't had the pleasure of meeting before. I'm the Community Development Manager for the element14 community. We are a global, external facing community for electronic design engineers. As a global community, language and localization are topics near and dear to our heart. We have done a modest amount of customization to the application, and a good deal of it has been in this area of language/localization specifically. For example, we have a widget that lets us display different information to a member based on his/her locale. We can also insert translations in this widget on the fly (avoiding having to add new things to the i18n files and do server restarts constantly). We've integrated Google Translate into our site (there is a white paper on how we did that out in Jivespace somewhere...), and gone through the painful process of adding support for langauges that Jive doesn't currently - like Traditional Chinese, Thai and Korean (we're on 4.5 now and I'm not looking forward to upgrading those I can tell you).
I'm really interested to meet other Jivers working on global communities and hear the challenges and solutions they've implemented within their own sites, if they're willing to share.