If you get on your site an error like this:
warning: file_get_contents(sites/default/files/languages/ar_bb3f64e1d3c493008e8d5eee5511c741.js) [function.file-get-contents]: failed to open stream: No such file or directory in /var/www/html/uberdrupal/includes/common.inc on line 2359.
Indeed Locale is unable to rebuild lost js translation files, if one of these gets accidentally corrupted or lost there is no way to tell Drupal to rebuild it. This is true in all versions of Drupal 6.x, the last too.
Reference: Drupal.org Issue.