Some Special Characters do not show on your device, it is caused by a little error while upgrading or reloading your OS, you forget to tick the language boxes. it can be fixed simple by installing those font language to your device.
Font OTA link for OS 4 supports OS 5, but there will be some Characters still un-show.
Font OTA link for OS 5 supports OS 6 as well (already tested on 9800)
Font Support (READ) For BlackBerry OS 4 Devices
Font Support (READ) For BlackBerry OS 5 Devices