@tryashtar, I share your opinion that IF the wiki is wrong, that the wiki should fix it. But no-one yet responded wether or not this was intended or not in the game. The minecraft wiki is of high quality. I won't believe they just write bullshit. They had some reason to include this, and maybe they included it because it was a feature in the past. At this point in time it is not clear wether the game has a unknown bug or the wiki messed something up. I report this as a potential bug. I would like to find out where the error is.
Therefore, I believe resolving this as an invalid bug report is way to soon. There is no information yet to close this.
I tested this in release 1.15.2. A wandering trader who uses a nether portal will still despawn in the nether after his DespawnDelay reaches 0. This works correctly. They do drink a potion of invisibility as soon as they arrive in the nether. I don't think this is weird behaviour though.