Hi,
As also written in changelog[1], the OTR plugin of kopete does not
compile with libotr 4.x (and the old libotr is planned to away soon),
and even upstream there are no fixes for that.
Considering the API changed a lot, porting it was not an option since it
required an amount of work.
I'm not sure what you refer wrt an "opnepgp plugin".
[1] /usr/share/doc/kopete/changelog.Debian.gz
--
Pino Toscano