The tag is present in Lintian version 2.104.318. That is the most recent version we know about.
debconf-updatepo has not been run since the last change to your debconf templates.
You should run debconf-updatepo whenever debconf templates files are changed so that translators can be warned that their files are outdated.
This can be ensured by running debconf-updatepo in the 'clean' target
debian/rules. PO files will then always be up-to-date when
building the source package.