Languages do not exist as unconnected entities; rather, every language will be related in some way to every other language…
Systems of measurement might not sound like the most interesting of things, but they can be used to good effect in a role play campaign. There are three main ways I can think of: 1) Adding colour; 2) Culture shock and 3) Archaic systems.
The spellbook of a long dead wizard that has gained the ability to read itself and cast spells from itself. If could be amazingly powerful as an ally, or use its magic to manipulate and rule a kingdom.