I'm not sure you understand what Dunning-Kruger is. Or I certainly don't see why that quote is an example of it.
The Dunning-Kruger effect doesn't necessarily imply a narcissistic personality (or any other personality traits); overconfidence in ability is something we are all vulnerable to.
I think if you "master a language", you don't get lumped in with those who know "a little bit". I think you're just talking about arrogant people in general who think that because they know X, they can berate those who don't know X.
Consider a person who plays, for example, a multiplayer game against the same three real life friends on a LAN, and concludes from his performance -- domination of his friends -- that he is an astounding player. Given his knowledge about the game and the skill of other players, it makes sense for him to make this conclusion. However, were he to play online, he would realize that his skills are paltry compared to the those of the best online gamers.
Here, Dunning-Kruger is manifested in this gamer's overconfidence based on lack of knowledge, and lack of meta-knowledge (he doesn't know the importance of what he doesn't know). It's based on a genuine mistake in his assessment of his skills, not necessarily arrogance.