I have been using $conf['i18n_variables'] = array(); in settings.php successfully for some time. I just updated my site from drupal 6.14 to 6.15 and now the i18n_variables section of the settings.php file seems to be ignored completely. I can remove the '$conf['i18n_variables']...' completely from settings.php and it doesn't make a difference despite how many times I run cron and update.php. If I remove settings.php completely, it complains so I know that the rest of the file is being used.
What's odd is that admin/settings/site-information still shows the 'site_name' and 'site_frontpage' sections with 'This is a multilingual variable' and when I update the values in the admin panel, they update in both db tables: i18n_variable and variable. These two seem to work fine as i18n_variables but none of the others are working - they are not showing up as multilingual variables and they are not being updated in the i18n_variable table at all, only in the variable table when values are changed.
I have carefully gone over the old/new settings.php files, reverted back to 6.14 and reinstalled, run cron and update. The rest of the site seems unaffected but I had been using $conf[... to specify 'site_slogan', 'site_footer', 'logo_path', none of which are now working. I did have to rebuild permissions when I updated to 6.15 but everything else seems ok.