Suppose a creature wants to create their own constructed language for purposes of obscuring communication. Are there any rules that would cover creating and learning such a conlang? For example, suppose my high-INT wizard were to create his own secret language, and wants to teach the language to the rest of the party in order to discourage others from eavesdropping.
- Can the other party members learn the language as they would any other (e.g. through downtime, a feat, etc.)?
- Is a conlang not a "real language" in terms of the rules, and the ability of anyone else to learn it would simply be by DM fiat?
I know that at the end of the day, all rulings are under the control of the DM, but I'm asking whether there exist rules to cover this sort of scenario or whether it is a lacuna. This could affect, for example, whether another creature could use Tongues to understand a conlang - if it is a "real" language, then the answer would probably be yes, if a conlang is simply an informal arrangement (not "really" a true language under the rules), then the answer would probably be no.