Two military friends create own language

[Bryn]

This would be from 2012 or shortly before. I believe both characters are veterans but it may be only one. I think i remember one of them being in New York while the other was overseas? They create their own language to communicate with each other. I think the title may include ‘dictionary’ or ‘encyclopedia’

[Kris]

Bryn, what is the story's time period? Which war?

Can you tell us more about the plot and the main characters? What's the genre?

Can you describe their language and how it worked? Examples? Did they exchange letters?