The tag is present in Lintian version 2.109.3. That is the most recent version we know about.
The following file source files include material under a non-free license from Unicode Inc. Therefore, it is not possible to ship this in main or contrib.
This license does not grant any permission to modify the files (thus failing DFSG#3). Moreover, the license grant seems to attempt to restrict use to "products supporting the Unicode Standard" (thus failing DFSG#6).
In this case a solution is to use libicu and to remove this code by repacking.
Please refer to Bug#823100 for details.