What about the strange language?

[ginny343]

No: HPFGUIDX 141963

While rereading part of HBP last night, I came across something that 
made me wonder.  When Harry and DD are headed back to the castle 
after noticing the dark mark this comment is made:

 "As they flew over the dark, twisting lane down which they had 
walked earlier, Harry heard, over the whistling of the night air in 
his ears, Dumbledore muttering in some strange language again.  He 
THOUGHT he understood why as he felt his broom shudder when they 
flew over the boundary wall into the grounds:  Dumbledore was 
undoing the enchantments he himself had set around the castle so 
they could enter at speed."

Okay, first, I know DD has done this before because the word "again" 
did not phase me when I read it, but I cannot find where.  If 
someone could remind me where it is, I would be grateful.

But here is the thing that has me wondering.  JKR writes "he thought 
he understood" not "he understood" . . . so that makes me think DD 
was muttering in some strange language for another reason.  And I 
wonder what it could be?  Or, I could just be reading too much into 
it . . . :)

Ginny343