While upgrading Open GreenMap from Drupal 5 to Drupal 6, we had to port the Taxonomy Limit module by codexmas, which restricts the number of taxonomy terms which can be chosen for a multiselect vocabulary. The author hasn't had time to create his own Drupal 6 version, so we at Openflows Community Technology Lab volunteered to become co-maintainers.
Notes from a talk on how to use i18n with Drupal 6 for people who have never done it before, presented at DrupalCamp Montreal in October 2008.
Start with this page from the handbook: Tutorial - Building a multi-language site. You have the choice of switching based on path prefix (with optional browser language detection when no prefix is specified) or domain name.
Other useful modules:
Use Administer / Content management / Translation overview to see which nodes require translation, and Administer / Site building / Translate interface to translate individual strings (e.g. a CCK field name).
