Fwd: what is this gtk that apt-listchanges uses ?

Hi all,
I am using apt-listchanges to view changelogs within each new update
of the package. Many a times when the changelog is being viewed, some
fonts show while others don't. I get the unicode replacement
character. See https://en.wikipedia.org/wiki/Replacement_character#Replacement_character

This is the configuration I use to view the changelogs :-

   [apt]
   frontend=gtk
   email_address=root
   confirm=1
   save_seen=/var/lib/apt/listchanges.db
   which=both

Now I know the fault is not in apt-listchanges but probably in the
frontend gtk. Can somebody tell me a bit about gtk that I have listed
therein. Which package or where does that link to ?

Any more info. would be nice.

I do have to point out though that I had actually asked the same
question/query on the debian fora and till
yet haven't got an answer hence asking the mailing list.

http://forums.debian.net/viewtopic.php?f=10&t=75683

Feel free to answer it either here or there on the forums (in either
case I will quote you and put it there in the fora (for others)
posterity as well).