Unfortunately, the html files are not in plain text. Up to 2.0.0 or so they were gz compressed. Since then they seem to be encrypted, I guess because of copyright concerns. The "words"-file seems to be an index file (I have no idea about the encoding).
I had some plans about manipulating dictionaries (
link) and I actually put some efforts into it. However, I gave up because of the encryption.
I still have a faint hope that the KT stores the html files in plain format on the system partition for performance reasons. Since I am a Ms Windows user without any knowledge of Linux I cannot access this partition. I would be thankful for any information.