Hi, and thanks for the report, and I'm sorry I failed to fix this before bullseye. I believe the proper fix is to build with --with-po- suffix so that the po files are called gss3.po in libgss-dev, instead of gss.po which caused the conflict you noticed. The --with-po-suffix parameter was mistakenly dropped in 1.0.3-5 which also explains why this happened now rather many years ago.
I'm fixing this for unstable/testing with a new upload. I'm thinking whether we also want to fix this in bullseye? Maybe a propsed-update upload? I have never done an upload like that, so I don't know what the requirements and restrictions are for fixes to a stable release. It does seem to make sense though, since it helps to fix multi-release upgrade paths. My upload now doesn't resolve why libgss0 is installed after a long- time upgrade cycle like yours. I'm not sure that is incorrect: having libgss0 installed (even when libgss3 is installed) is fine and shouldn't cause problems. Are packages required to make sure old obsolete packages are removed? If so, is a Replaces: libgss0 on libgss3 sufficient? What do you think? /Simon