UnicodeDecodeError while logging

Running the i18n_tool validate command kept failing because of some UnicodeDecodeError that occurred when logging the problem with the .po file

Traceback (most recent call last):
  File "/edx/app/edxapp/venvs/edxapp/bin/i18n_tool", line 11, in <module>
    sys.exit(main())
  File "/edx/app/edxapp/venvs/edxapp/local/lib/python2.7/site-packages/i18n/main.py", line 60, in main
    return module.main()
  File "/edx/app/edxapp/venvs/edxapp/local/lib/python2.7/site-packages/i18n/__init__.py", line 51, in __call__
    return self.run(args)
  File "/edx/app/edxapp/venvs/edxapp/local/lib/python2.7/site-packages/i18n/validate.py", line 250, in run
    if validate_po_files(self.configuration, locale_dir, report_empty=args.empty, check_all=args.check_all):
  File "/edx/app/edxapp/venvs/edxapp/local/lib/python2.7/site-packages/i18n/validate.py", line 43, in validate_po_files
    if msgfmt_check_po_file(locale_dir, filename):
  File "/edx/app/edxapp/venvs/edxapp/local/lib/python2.7/site-packages/i18n/validate.py", line 80, in msgfmt_check_po_file
    log.warning(u'\n' + err.decode('utf8'))
  File "/edx/app/edxapp/venvs/edxapp/lib/python2.7/encodings/utf_8.py", line 16, in decode
    return codecs.utf_8_decode(input, errors, True)
UnicodeDecodeError: 'utf8' codec can't decode byte 0xd0 in position 328: invalid continuation byte

This was the error(err) that it was trying to log in log.warning(u'\n' + err.decode('utf8'))

../../Desktop/Project/i18n-tools/i18n/django-partial.po:6509: 'msgstr' is not a valid Python brace format string, unlike 'msgid'. Reason: In the directive number 0, there is an unterminated format directive.\n../../Desktop/Project/i18n-tools/i18n/django-partial.po:9602: 'msgstr' is not a valid Python brace format string, unlike 'msgid'. Reason: In the directive number 0, '\xd0' cannot start a field name.\n../../Desktop/Project/i18n-tools/i18n/django-partial.po:12407: 'msgstr' is not a valid Python brace format string, unlike 'msgid'. Reason: In the directive number 0, '\xd0' cannot start a field name.\nmsgfmt: found 3 fatal errors\n"
663
../../Desktop/Project/i18n-tools/i18n/django-partial.po:6509: 'msgstr' is not a valid Python brace format string, unlike 'msgid'. Reason: In the directive number 0, there is an unterminated format directive.
../../Desktop/Project/i18n-tools/i18n/django-partial.po:9602: 'msgstr' is not a valid Python brace format string, unlike 'msgid'. Reason: In the directive number 0, '�' cannot start a field name.
../../Desktop/Project/i18n-tools/i18n/django-partial.po:12407: 'msgstr' is not a valid Python brace format string, unlike 'msgid'. Reason: In the directive number 0, '�' cannot start a field name.
msgfmt: found 3 fatal errors

Since the filename or language code was not getting logged for which the validation was failing on jenkins pull_translations job it was particularly difficult to find the file and issue.

Start in i18n/validate.py at msgfmt_check_po_file, especially the log.warning call around line 80, and reproduce the failure with i18n_tool validate on the reported .po file. Check that validation errors can be logged without a UnicodeDecodeError and that the failing filename or language code is identifiable in the output.