So it appears that the LANGUAGE=... variable takes precedence over LANG and LC_* although it's not a GUI application, and of course, ubuntu-support-status does not have a man page where this could be documented, and update-manager also does NOT document or reference this variable in an "ENVIRONMENT" section.
Workaround: run:
env LC_ALL=C LANGUAGE= ubuntu- support- status
or
env LANGUAGE=en ubuntu- support- status
So it appears that the LANGUAGE=... variable takes precedence over LANG and LC_* although it's not a GUI application, and of course, ubuntu- support- status does not have a man page where this could be documented, and update-manager also does NOT document or reference this variable in an "ENVIRONMENT" section.