Here is a (brief) list of languages for my homebrew setting. As is my wont, I eschew common fantasy languages like Elvish. Instead, the following languages are spoken and written in the Low Kingdoms...
Half-Tongue. The pidgin language of the fey. It's a dialect of Common and the First Speech that changes with every speaking. No two sentences are alike, even if they have the same meaning.
Old Common. The florid language of the Old Empire. Mainly used by scholars.
Malifigua. This despicable tongue is said to be taught by demons to their infernal followers. For those who cannot understand, it is nauseating to hear.
Norf. The vulgar language of T'ill North.
Sermon Form. A coded dialect used by ecclesiastical scholars. It has been largely forgotten, except to conceal heretical works. Written only.
Solemn. The whispered language spoken amongst the dead. Non-speakers can't even hear this tongue, which sounds like indistinct mumblings to them.