Well, the dialogues work now and I also have the new UI by default.
However, icons still don't work and keyboard shortcuts don't either :(
Maybe I should wait for a stable Inkscape build for Debian.
Maybe, but think of it: others do not have your problems so there
must be a reason. It is not clear from your reply if you applied
everything advised: remove $HOME/.inkscape/ and make install from
your source.
ralf