This summary is not the rule. The rule text controls.
If someone has been fully interdicted by a court, it means a judge has decided they cannot manage their own affairs and need someone else to act for them legally. Because of this, the interdicted person cannot file a lawsuit on their own. The same applies to someone under a limited interdiction if the court order specifically takes away their right to sue.
Instead, a person called a curator has to file the lawsuit on their behalf. The curator is the person the court has put in charge of handling the interdicted person's legal and financial matters. This means if someone needs to sue to protect the interdicted person's rights, the curator is the one who must bring that case to court, not the interdicted person themselves.
There are a few exceptions written into other parts of the law (Articles 4431, 4554, and 4566) that can change who is allowed to sue in certain situations. So while the curator usually handles these lawsuits, it is worth checking those specific articles if there is a question about who has the right to sue in a particular case.