Period Speech
by Berg
Image Text: The same people who spend their weekends at the Blogger Reenactment Festivals will whine about the anachronisms in historical movies, but no one else will care.
Ah, language- the great social agreement of symbolic representation which enables someone like me, sitting in Los Angeles to communicate with someone like you, who I presume lives somewhere on the internet (nice place, by the way, but you should put your porn away before you have people over). Today's xkcd is about the inherent slipperiness of language, and how very little of what we say today will sound coherent to a future observer.
Consider English. Modern English is thought to have settled into it's current form (more or less) sometime in the 16th century. Before Modern English, however, were Middle English (mayhap you've heard of the Canterbury Tales?) and Old English (mayhap you've heard of Beowulf?). Middle English is close enough to Modern English that you can almost read it, but Old English is far enough away, linguistically, that it requires some study to be able to read.
The point xkcd is making, then, is that 400 years from now, bits of dialect and slang that to us seem quite disparate ("forsooth" is hundreds of years old, while "grok" entered the lexicon in '61) will seem quite similar to all but the most avid linguistic scholars. After all, if you were presented with 5th century slang and 9th century slang, chances are you wouldn't notice any difference.
Those who would notice the difference are addressed in the image text- they'll be the folks at the Blogger Reenactment Festivals. Those aren't a thing yet, but we can imagine that these would be fringe affairs, attended by only the most devoted of nerds (a term brought into the language by none other than Dr. Seuss in 1950). As such, their opinions as to the accuracy of slang presented in historical movies from the future represent the minority view, even if it is correct.

July 26th, 2010
The line about blogger reenactments is also an in-joke referencing comic #239 (”Blagofaire”).
July 27th, 2010
Is there a translation of what the characters are saying in the comic? I know 10-4 means “yes”, so they’re answering yes to the question he asks.
Hearties I assume is “friends”, and jive if I remember correctly would be something that someone says.
Although, jiving means lying in black slang.
July 28th, 2010
More or less (depending on which dictionary definition one chooses) it says, “Indeed, do you completely understand my jargon filled speech?”
Of course, one can take a more cynical approach and interpret it: “I do not think you understand my music.”
July 28th, 2010
The word ‘grok’ comes from the book “Stranger in a Strange Land”, by Robert A. Heinlein, originally published in 1961. At its most basic it means ‘to understand’, but a deeper meaning would be almost oriental in flavor: that you are at one with his jive.
Forsooth comes from Middle English (c. 1000-1470 C.E. (C.E. = A.D. but more politically correct)), meaning ‘in truth’, or ‘indeed’.