Success for me. I installed kompozer from that repository you mentioned. Kompozer version is 0.8a4. I tried installing language pack from kompozers main language pack page, and it was for a different version, so it wouldn't install. You don't need to install the language pack as root.Go Here
, download your choice, and:
extra>add-on>extensies>installeren>and go to where you downloaded .xpi file>open>nu installeren. That should do it.
Regards, Lisa Marie