Against either candlepin hosted or standalone, set your LANG env var to de_DE and run subscription-manager-cli register with a bad username/pass combo (for standalone you'll have to edit your config to include an auth line).
UnicodeEncodeError: 'ascii' codec can't encode character u'\xfc' in position 23: ordinal not in range(128)
A nice message in german about invalid username/password.
Note that the gui handles this fine, as does the log entry.
*** This bug has been marked as a duplicate of bug 590094 ***