Cloud and Squall posted...
Actually, Dumbledore does speak Pareltonuge. At least enough. More than Ron, who also gets into the chamber of secrets pretty easily. He demonstrates the ability in the memory with Bob Ogden.
For starters, Ron is a mimic. Actually, it's a bit of a Weasly thing--Ginny flawlessly mimics Umbridge's "Hem hem".
As for Dumbledore, I remember nothing in that chapter that demonstrates he understands Parseltongue. His lines are...
"You understand him, I'm sure, Harry?"
To me, this line always hinted that Dumbledore did NOT understand them, unlike Harry.
"Very good." (Telling Harry that yes: he's speaking parseltongue)
"I think that will do, Harry" (end of scene)
And then they discuss the scene in general terms, basically just Dumbledore telling Harry who the people were in the scene, not going into any detail until....
"Yes, that was Tom Riddle senior, the handsome Muggle who used to go riding past the Gaunt cottage and for whom Merope Gaunt cherished a secret, burning passion."
While the vast majority of the conversation was held in English, the fact that she had a crush on him was conducted in parseltongue. So...this is the one tidbit where it seems like Dumbledore understood the conversation.
Then again, the fact that she eventually got married to Tom Riddle would be a matter of public record; most likely Dumbledore could deduce a crush. And a good deal could be determined from body language--without being able to understand Parseltongue, you'd be able to tell that Morphin accused Merope of something, Merope goes white, Morphin continues, Merope tries to shake her head to tell him not to reveal anything, Marvolo gets angry, Merope shakes her head frantically, Marvolo strangles Merope. And all this is right after Tom Riddle calls a girl "darling" as he's passing.
So...I can maybe see this as evidence that Dumbledore knows Parseltongue, but there are so many other hints that it's also plausible that he doesn't.
"I think you are forgetting that Merope was a witch. I do not believe that her magical powers appeared to their best advantage when she was being terrorized by her father. Once Marvolo and Morfin were safely in Azkaban, once she was alone and free for the first time in her life, then, I am sure, she was able to give full rein to her abilities and to plot her escape from the desperate life she had for eighteen years."
And given that Marvolo called Merope a squib in English (not parseltongue) when he was tormenting her in front of Bob Ogden, I don't see anything here that Dumbledore would have needed parseltongue to deduce.
And then Dumbledore moves on to events that happened months or years later--not part of the memory at all.
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Cats land on their feet. Toast lands peanut butter side down. A cat with toast strapped to its back will hover above the ground in a state of quantum indecision