You should not mark as translatable "Default:" or "DefaultChoice:" fields, unless explicitly needed (e.g. default country, default language, etc.). If this Default field really should be translated, you should explain translators how they should translate it by using comments or brackets. For example:
# Translators: Default language name, but not translated _Default: English
_Default: English[ Default language name, but not translated]
Note that in the first case, Lintian ignores the comment unless it explicitly references translators and it is appears directly before the field in question.
For more information please consult:
The tag is present in Lintian version
That is the most recent version we know about.
We use semantic versions.
The patch number is a commit step indicator relative to the
release tag in our Git
You can find the detection logic for this version at commit ea05801. For merge requests, please use the latest version in the Lintian check debian/po-debconf.