The Symbian OS is from the ground up based on Unicode.
A particular phone might not have Unicode fonts with all languages as part of the firmware, but they might be installed afterwards.
A hard reset might (and probably does) remove fonts from phone memory that are not in ROM (read-only memory).
A firmware update might restore them, if the fonts are part of the firmware update.
Otherwise, a firmware update might also cause languages to be lost, if the firmware has been updated to a different language variant after the phone left the factory: