This just popped in my head, and being the nerd I am I thought of the Romulan and Vulcan peoples; coming from a common ancestor, but over many generations their language and even biology drifted apart.

Obviously biology isn't the point (unless it is, let me know), but over 2 or 3 generations of being separate the languages must have diverged somewhat; especially with one being introduced to the world forum, while the other has not