I had once attempted to synthesize the systems from the Tome of Magic and Testament while simultaneously upgrading the result to the Pathfinder revision. I have lost those rules, but do recall not exactly being pleased with the direction I was going. It is not the easiest style of magic to present for tabletop RPGs--typically when every individual has their own true name. This would explain the universal language concept used in Tome of Magic. Paizo would later revisit a similar concept with their Words of Power system in Ultimate Magic.
Recently, Wizards has revisited true name magic for 5th Edition in an Unearthed Arcana supplement. Here, it is called onomancy. Below, I show how onomancy can have a place in my 5th Edition campaign setting, Monvesia.
Ren-HekaIn Raviq--among the neshu, dogfolk, and cattlefolk--onomancy is known as ren-heka. Loosely translated from the Neshu language, this means "name magic." Names are both protected and revered throughout the remaining humanoid races of Raviq. While the practice of divining true names originated with the Neshu, it was the Anepu (dogfolk) who learned the secrets of creating or even destroying names. Any corpse interred without a name is doomed to rise again as undead, unable to escape the Abyss into the promised afterlife.
The Neshu court onomancers (commonly referred to as "name priests") maintain lists of the true names of kins and high priests--but will only add a name after the death of the individual named. Moreover, the name is record as soon after death as possible in order to preserve the name from being erased by Anepu death necromancers.
New Feat: Adept Onomancer
New Spell: Unname
Casting Time: 1 action
Range: 150 feet
Components: V (including a true name), M (any method with which to write with he ability to destroy or deface the writing)
You record and deface or destroy the true name of a creature that you can see within range, attempting to erase its name and disrupt its emotional stability. The target takes 5d6 necrotic damage and must make a Wisdom saving throw.
On a failed save, the creature's Wisdom and Charisma scores become 1. The creature cannot cast spells, activate magic items, or even be reincarnated or resurrected (without a true name, a soul is unable to return to is body). Anyone who has learned the creature's true name will no longer be able to use that name to affect the creature.
At the end of every 30 days, the creature can repeat its saving throw against this spell. If i succeeds on is saving throw, he spell ends. The creatures true name is not restored; instead, it gains a new true name--which must be learned by anyone who previously knew the old name.
The spell can also be ended by greater restoration or wish.
True NamesThere is disagreement among cultures as to what constitutes a true name. The simplest answer is that one's true name is the one by which they personally identify. However, a major theme of the Monvesia setting is perception--how a character is seen by others affects the way that character inerracts with the world (such as through alignment or the Taint). Therefore, in Monvesia at least, a true name will also include the name by which a character is best known.
True names are not short and sweet epithets, but extensive descriptors. To know someone's true name is to know what they are called by any who know them. This may include given names, chosen names, ritual names, professional names, patronyms, matronyms, family names, house names, and so forth. For example, a ruling queen's true name would include her regnal name, her birth name, and even the name of her house/lineage/dynasty--even though all these components would not be used together in life. Missing but one of these components will result in failure to call on the person's true nature--as would stringing these components together in the wrong order.
The true name of Disney's Aladdin would include both that name and his chosen name, Ali Ababwa. The true name of the early protagonist of Frank Herbert's Dune novels would include: his birth name, Paul; his house name, Atreides; and his Fremen names, Usul and Muad'Dib.