Board Thread:Lore Discussion/@comment-209.107.228.80-20130202223430/@comment-9887604-20130618132017

The Argonian native language is Jel, which is the closest thing to thought. Non Argonians can learn it kind of, but can not converse coherently. They refer to themselves as the Saxhleel in their own languange.

Its also important to remember the Dwemer had a form of telepathy, named the Calling.

The Ayelids language is referred to as old Cyrodiilic. Off topic Cyrodiil is an Ayelid word meaning heartland.

Khajiit native language is Ta'agra

I think it would be an endless task, and one that would be mostly conjecture to try and decide most of the languages not mentioned directly in game. It's as broad a topic as you want it to be.