The tag is present in Lintian version 2.104.328. That is the most recent version we know about.
This debconf translation is using the general debconf-i18n list as the address in the Language-Team field.
The intended purpose of the Language-Team field is to be an additional contact for new translation requests in addition to the previous translator (as recorded in Last-Translator). The field should therefore point to a mailing list dedicated to the language of this PO file, not the general list for translation discussions.