I knew everyone including dragons call Dovahkiin as Dragonborn, but base on http://www.uesp.net/wiki/Lore:Dragon_Language#Q it has 3 possible combination:

"Dovah", "Kiin" = "Dragon", "Born"

"Do", "Vah", "Kiin" = "About", "Spring", "Child"

"Dov", "Ah", "Kiin" = "Wyrm", "Hunter", "Child"

So if we combine these, it might means "One of the child who born during Spring has dragon blood flow in vein and that child is destined to hunt down dragons".

DLC content is to discover the mystery of Dragonborn background story? Just guessing

Who presumes to know the Dragon tongue better that the Dragons?

Well the Wyrm hunter makes since. The Spring child part sounds hippie-ish.