Here are some basic ways to add and incorporate the fantasy elements of truenames to 5th edition while retaining some of the crunch of the past.
What are Truenames?
Truenames are the names of all things in the mother language of the universe. They are the nouns and verbs in the tongue of the worlds creation. Every creature, object, or location has a truename. All part of the previous has trunames. Truenames describe what a subject is at the current moment.
No one except maybe deities can speech it. Only a overdeity or the deity who created the universe can ever be fluent because of the power of the language.
Anything spoken with the truename of a subject and correctly in the language just happens to the subject. Reality simply warps to make the statement true. The subject itself cannot resist. The battle is purely between the speaker and the universe itself. All one can do it hide their truename and alter it if ever becomes known. Those who study the art of speaking and researching the truenames of the universe are called truenamers.
Truenames and Creatures.
Every creature individually has it's own truename. When its truename is spoken, the creature knows. Commands to it are nearly irresistible and commands in the the full language of the universe are completely so.
However, a truename is the name of a being or object in this current state. Some creatures and items can fundamentally change and their truenames change with them. Other creatures, usually immortals, cannot change with their own destruction as a result and their truenames never change.
Glossary
Lexicon: One of the many categories of utterances. Equivalent to a school of spells.
Permission: The right to speak another's personal truename. Permission always originates for the owner of the truename.
Personal Truename: The truename that describes a unique individual.
Recitation: The repetition of a personal truename to restore itself to its original state usually to cure curses, poisons, and wounds.
Truename: The description of a creature, object, place, or action in the language of the universe.
Truespeak: The skill to correctly pronounce truenames. One needs proficient to speak any personal truename without a permission.
Unchanging: Beings whose truenames normally cannot change. Celestials, fey, and fiends are unchanging.
Utterance: A combination of phrases with a truename describing an action. They are equivalent to cantrips which ignore spell resistant and failure due to target's actions or reactions.
Speaking a Truename.
Speaking truenames is hard. However it is just speaking so reattempts until success are infinite. Speaking a truename, recitation, or utterance is a Intelligence (Truepeak) check vs a DC based on the target.
The DC to speak a creature's truename aloud is 15 + double the creature's proficiency modifier.
The DC to speak a nonmagical item's truename aloud is 15.
The DC to speak a common or uncommon magic item's truename aloud is 20.
The DC to speak a rare or very rare magic item's truename aloud is 25.
The DC to speak a legendary magic item's truename aloud is 30.
Speaking a personal truename aloud is done at disadvantage unless it directly spoken to you by the owner which in this case is done at advantage. Speaking a creature's truename without a form of permission or proficiency in Truepeak is impossible. The universe hears all, even in silence. Speaking a truename in an area affected by the silence spell can still be done but at disadvantage.
Truename Research and Permissions
Research of personal truenames is hard. It takes a number of weeks equal to double the subject's proficiency modifier to fully research a personal truename to the point it can be spoken aloud. During each week, an equivalence of 1000 gp of resources must be spent. The time and thus cost can be reduced various ways. Access to a grand library or a staff of assistants reduce the time by a week each. Knowing the subject's ancestors reduces the time by one week per generation above you know. Casting the commune, divination, legend lore during any of the weeks reduces the research time by one week each.
After the first week of research, the universe and the subject are both nudge by your attempts to learn its personal truname. Most normal people have no idea what the feeling means but the unchanging always do. Evil beings often strike before the process is complete. Good being do things to make research of their names harder and more dangerous.
The faster, cheaper, and safer way to learn a personal truename is from permission. A being tell another their personal truename and the recipient can tell or write it down for others to learn. This is permission. In fact, the only way to discover a truename except your own or of the unchanging is to find a person or the writings of a person who was given permission or to be proficient in Truespeak.
Truenaming and your game.
The main use of truenaming in games without actual truenamers is dealing with fiends. Fiends traffic in truenames. Mortals bind demons, deamons, and devils with truenames. Fiends steal the souls of mortals by learning their truenames. Even with their long lives, fey, fiends, and celestials rarely even learn to Truespeak. The process typically is an easy way to get all your enemies to attack. An angel who can Truespeak is a danger to all the Hells, Abyss, and all below. And the reverse is true. So research is a quick way to Armageddon or assassination.
The lower respect of mortals by immortals gives them more leeway. And by the time a mortal truenamer becomes a master, few of the smart immortal beings risk introduction. So when a researcher starts looking up names in order to stop an invasion, most see it as a problem for the subject and the subject alone. But the seriousness of the matter to the subject forces the subject to act. Adventurers are often called to find rare tomes or protect researchers from their subjects.
What are Truenames?
Truenames are the names of all things in the mother language of the universe. They are the nouns and verbs in the tongue of the worlds creation. Every creature, object, or location has a truename. All part of the previous has trunames. Truenames describe what a subject is at the current moment.
No one except maybe deities can speech it. Only a overdeity or the deity who created the universe can ever be fluent because of the power of the language.
Anything spoken with the truename of a subject and correctly in the language just happens to the subject. Reality simply warps to make the statement true. The subject itself cannot resist. The battle is purely between the speaker and the universe itself. All one can do it hide their truename and alter it if ever becomes known. Those who study the art of speaking and researching the truenames of the universe are called truenamers.
Truenames and Creatures.
Every creature individually has it's own truename. When its truename is spoken, the creature knows. Commands to it are nearly irresistible and commands in the the full language of the universe are completely so.
However, a truename is the name of a being or object in this current state. Some creatures and items can fundamentally change and their truenames change with them. Other creatures, usually immortals, cannot change with their own destruction as a result and their truenames never change.
Glossary
Lexicon: One of the many categories of utterances. Equivalent to a school of spells.
Permission: The right to speak another's personal truename. Permission always originates for the owner of the truename.
Personal Truename: The truename that describes a unique individual.
Recitation: The repetition of a personal truename to restore itself to its original state usually to cure curses, poisons, and wounds.
Truename: The description of a creature, object, place, or action in the language of the universe.
Truespeak: The skill to correctly pronounce truenames. One needs proficient to speak any personal truename without a permission.
Unchanging: Beings whose truenames normally cannot change. Celestials, fey, and fiends are unchanging.
Utterance: A combination of phrases with a truename describing an action. They are equivalent to cantrips which ignore spell resistant and failure due to target's actions or reactions.
Speaking a Truename.
Speaking truenames is hard. However it is just speaking so reattempts until success are infinite. Speaking a truename, recitation, or utterance is a Intelligence (Truepeak) check vs a DC based on the target.
The DC to speak a creature's truename aloud is 15 + double the creature's proficiency modifier.
The DC to speak a nonmagical item's truename aloud is 15.
The DC to speak a common or uncommon magic item's truename aloud is 20.
The DC to speak a rare or very rare magic item's truename aloud is 25.
The DC to speak a legendary magic item's truename aloud is 30.
Speaking a personal truename aloud is done at disadvantage unless it directly spoken to you by the owner which in this case is done at advantage. Speaking a creature's truename without a form of permission or proficiency in Truepeak is impossible. The universe hears all, even in silence. Speaking a truename in an area affected by the silence spell can still be done but at disadvantage.
Truename Research and Permissions
Research of personal truenames is hard. It takes a number of weeks equal to double the subject's proficiency modifier to fully research a personal truename to the point it can be spoken aloud. During each week, an equivalence of 1000 gp of resources must be spent. The time and thus cost can be reduced various ways. Access to a grand library or a staff of assistants reduce the time by a week each. Knowing the subject's ancestors reduces the time by one week per generation above you know. Casting the commune, divination, legend lore during any of the weeks reduces the research time by one week each.
After the first week of research, the universe and the subject are both nudge by your attempts to learn its personal truname. Most normal people have no idea what the feeling means but the unchanging always do. Evil beings often strike before the process is complete. Good being do things to make research of their names harder and more dangerous.
The faster, cheaper, and safer way to learn a personal truename is from permission. A being tell another their personal truename and the recipient can tell or write it down for others to learn. This is permission. In fact, the only way to discover a truename except your own or of the unchanging is to find a person or the writings of a person who was given permission or to be proficient in Truespeak.
Truenaming and your game.
The main use of truenaming in games without actual truenamers is dealing with fiends. Fiends traffic in truenames. Mortals bind demons, deamons, and devils with truenames. Fiends steal the souls of mortals by learning their truenames. Even with their long lives, fey, fiends, and celestials rarely even learn to Truespeak. The process typically is an easy way to get all your enemies to attack. An angel who can Truespeak is a danger to all the Hells, Abyss, and all below. And the reverse is true. So research is a quick way to Armageddon or assassination.
The lower respect of mortals by immortals gives them more leeway. And by the time a mortal truenamer becomes a master, few of the smart immortal beings risk introduction. So when a researcher starts looking up names in order to stop an invasion, most see it as a problem for the subject and the subject alone. But the seriousness of the matter to the subject forces the subject to act. Adventurers are often called to find rare tomes or protect researchers from their subjects.