So mephits/the scamps that replaced them are said to work in groups of mixed elements sometimes (like it is said in the Wood Scamp entry), but how does that work? They have language, but they are specific to the plane. An Earth Scamp speaking Petran can't talk to a Water Scamp speaking Thalassic, right? There's no common language for them listed.
Archives of Nethys says they have long titles are part of their name to show off to other scamps/mephits and their master, but can they actually communicate that to their summoner? Will your average witch or wizard learn Muan to talk to their familiar? How do they convey these names and titles.
Will your average witch or wizard learn Muan to talk to their familiar?
I can't speak to the rest of that, but this I at least know. The Witch or Wizard or other person with a familiar can use the Speech ability to have them speak a language that the master does know.
Scamp Familiars have the Speech Familiar Ability, so they speak a language their master understands (in general common). Also, my Witch speaks Ignan. I think it's rather common for a high Int character to speak the language of the plane of their Familiar (as chances are high you don't have a Scamp Familiar by chance...).