The package has a debian/watch file, but the last attempt
to use it for checking for newer upstream versions failed with
an error:
In debian/watch no matching files for watch line https://ja.osdn.net/projects/nkf/releases/ /projects/nkf/downloads/\d*/nkf-[-_](\d[\-+\.:\~\da-zA-Z]*)(?i)\.(?:tar\.xz|tar\.bz2|tar\.gz|zip)/ debian uupdate
The URL(s) for this package had some recent persistent
issues.