/var/log/dist-upgrade/apt-term.log does not contain all the (error) messages what was on the screen during do-release-upgrade.

I have found in /var/log/syslog a "Falling back to the standard locale ("C")":

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Nov  7 16:57:47 - org.debian.apt[893]: /usr/lib/python3/dist-packages/aptdaemon/worker/pkworker.py:35: PyGIWarning: PackageKitGlib was imported without specifying a version first. Use gi.require_version('PackageKitGlib', '1.0') before import to ensure that the right version gets loaded.
Nov  7 16:57:47 - org.debian.apt[893]:   from gi.repository import PackageKitGlib as pk
Nov  7 16:57:47 - org.debian.apt[893]: 16:57:47 AptDaemon [INFO]: CommitPackages() was called: dbus.Array([dbus.String('python3-netifaces#auto')], signature=dbus.Signature('s')), dbus.Array([dbus.String('')], signature=dbus.Signature('s')), dbus.Array([dbus.String('')], signature=dbus.Signature('s')), dbus.Array([dbus.String('')], signature=dbus.Signature('s')), dbus.Array([dbus.String('kmod'), dbus.String('libkmod2'), dbus.String('libxkbcommon-x11-0'), dbus.String('libxkbcommon0'), dbus.String('module-init-tools'), dbus.String('openssh-client'), dbus.String('ppp')], signature=dbus.Signature('s')), dbus.Array([dbus.String('')], signature=dbus.Signature('s'))
Nov  7 16:57:47 - AptDaemon.Trans: INFO: Queuing transaction /org/debian/apt/transaction/fe6ec1c7a6bc44b7adfc9ccc71fdec0c
Nov  7 16:57:47 - org.debian.apt[893]: 16:57:47 AptDaemon.Trans [INFO]: Queuing transaction /org/debian/apt/transaction/fe6ec1c7a6bc44b7adfc9ccc71fdec0c
Nov  7 16:57:47 - AptDaemon.Worker: INFO: Simulating trans: /org/debian/apt/transaction/fe6ec1c7a6bc44b7adfc9ccc71fdec0c
Nov  7 16:57:47 - org.debian.apt[893]: 16:57:47 AptDaemon.Worker [INFO]: Simulating trans: /org/debian/apt/transaction/fe6ec1c7a6bc44b7adfc9ccc71fdec0c
Nov  7 16:57:48 - AptDaemon.Worker: INFO: Committing packages: dbus.Array([dbus.String('python3-netifaces#auto')], signature=dbus.Signature('s')), dbus.Array([], signature=dbus.Signature('s')), dbus.Array([], signature=dbus.Signature('s')), dbus.Array([], signature=dbus.Signature('s')), dbus.Array([dbus.String('kmod'), dbus.String('libkmod2'), dbus.String('libxkbcommon-x11-0'), dbus.String('libxkbcommon0'), dbus.String('module-init-tools'), dbus.String('openssh-client'), dbus.String('ppp')], signature=dbus.Signature('s')), dbus.Array([], signature=dbus.Signature('s'))
Nov  7 16:57:48 - org.debian.apt[893]: 16:57:48 AptDaemon.Worker [INFO]: Committing packages: dbus.Array([dbus.String('python3-netifaces#auto')], signature=dbus.Signature('s')), dbus.Array([], signature=dbus.Signature('s')), dbus.Array([], signature=dbus.Signature('s')), dbus.Array([], signature=dbus.Signature('s')), dbus.Array([dbus.String('kmod'), dbus.String('libkmod2'), dbus.String('libxkbcommon-x11-0'), dbus.String('libxkbcommon0'), dbus.String('module-init-tools'), dbus.String('openssh-client'), dbus.String('ppp')], signature=dbus.Signature('s')), dbus.Array([], signature=dbus.Signature('s'))
Nov  7 16:57:48 - org.debian.apt[893]: perl: warning: Setting locale failed.
Nov  7 16:57:48 - org.debian.apt[893]: perl: warning: Please check that your locale settings:
Nov  7 16:57:48 - org.debian.apt[893]: #011LANGUAGE = (unset),
Nov  7 16:57:48 - org.debian.apt[893]: #011LC_ALL = (unset),
Nov  7 16:57:48 - org.debian.apt[893]: #011LANG = "C.UTF-8"
Nov  7 16:57:48 - org.debian.apt[893]:     are supported and installed on your system.
Nov  7 16:57:48 - org.debian.apt[893]: perl: warning: Falling back to the standard locale ("C").
Nov  7 16:57:48 - org.debian.apt[893]: locale: Cannot set LC_CTYPE to default locale: No such file or directory
Nov  7 16:57:48 - org.debian.apt[893]: locale: Cannot set LC_MESSAGES to default locale: No such file or directory
Nov  7 16:57:48 - org.debian.apt[893]: locale: Cannot set LC_COLLATE to default locale: No such file or directory
Nov  7 16:57:55 - AptDaemon.Worker: INFO: Processing transaction /org/debian/apt/transaction/fe6ec1c7a6bc44b7adfc9ccc71fdec0c
Nov  7 16:57:55 - org.debian.apt[893]: 16:57:55 AptDaemon.Worker [INFO]: Processing transaction /org/debian/apt/transaction/fe6ec1c7a6bc44b7adfc9ccc71fdec0c
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