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bzr: ERROR: exceptions.TypeError: first argument must be string or compiled pattern

Traceback (most recent call last):
  File "/usr/lib/python2.7/site-packages/bzrlib/commands.py", line 930, in exception_to_return_code
    return the_callable(*args, **kwargs)
  File "/usr/lib/python2.7/site-packages/bzrlib/commands.py", line 1121, in run_bzr
    ret = run(*run_argv)
  File "/usr/lib/python2.7/site-packages/bzrlib/commands.py", line 673, in run_argv_aliases
    return self.run(**all_cmd_args)
  File "/usr/lib/python2.7/site-packages/bzrlib/commands.py", line 697, in run
    return self._operation.run_simple(*args, **kwargs)
  File "/usr/lib/python2.7/site-packages/bzrlib/cleanup.py", line 136, in run_simple
    self.cleanups, self.func, *args, **kwargs)
  File "/usr/lib/python2.7/site-packages/bzrlib/cleanup.py", line 166, in _do_with_cleanups
    result = func(*args, **kwargs)
  File "/usr/lib/python2.7/site-packages/bzrlib/builtins.py", line 1521, in run
    to_repo.fetch(br_from.repository, revision_id=revision_id)
  File "/usr/lib/python2.7/site-packages/bzrlib/vf_repository.py", line 1268, in fetch
    find_ghosts=find_ghosts, fetch_spec=fetch_spec)
  File "/usr/lib/python2.7/site-packages/bzrlib/decorators.py", line 218, in write_locked
    result = unbound(self, *args, **kwargs)
  File "/usr/lib/python2.7/site-packages/bzrlib/vf_repository.py", line 2585, in fetch
    find_ghosts=find_ghosts)
  File "/usr/lib/python2.7/site-packages/bzrlib/fetch.py", line 77, in __init__
    self.__fetch()
  File "/usr/lib/python2.7/site-packages/bzrlib/fetch.py", line 98, in __fetch
    pb.update(gettext("Finding revisions"), 0, 2)
  File "/usr/lib/python2.7/site-packages/bzrlib/i18n.py", line 40, in gettext
    install()
  File "/usr/lib/python2.7/site-packages/bzrlib/i18n.py", line 92, in install
    _translations = install_translations(lang)
  File "/usr/lib/python2.7/site-packages/bzrlib/i18n.py", line 114, in install_translations
    fallback=True)
  File "/usr/lib/python2.7/gettext.py", line 560, in translation
    t = _translations.setdefault(key, class_(fp))
  File "/usr/lib/python2.7/gettext.py", line 256, in __init__
    self._parse(fp)
  File "/usr/lib/python2.7/gettext.py", line 393, in _parse
    self.plural = c2py(plural)
  File "/usr/lib/python2.7/gettext.py", line 178, in c2py
    result, nexttok = _parse(_tokenize(plural))
  File "/usr/lib/python2.7/gettext.py", line 115, in _parse
    nexttok = next(tokens)
  File "/usr/lib/python2.7/gettext.py", line 86, in _tokenize
    for mo in re.finditer(_token_pattern, plural):
  File "/usr/lib/python2.7/re.py", line 190, in finditer
    return _compile(pattern, flags).finditer(string)
  File "/usr/lib/python2.7/re.py", line 247, in _compile
    raise TypeError, "first argument must be string or compiled pattern"
TypeError: first argument must be string or compiled pattern

bzr 2.7.0 on python 2.7.13 (Linux-4.10.13-1-pae-i686-with-glibc2.0)
arguments: ['/usr/bin/bzr', 'branch', 'lp:ctwm', 'trunk']
plugins: bash_completion[2.7.0], changelog_merge[2.7.0], grep[2.7.0],
    launchpad[2.7.0], netrc_credential_store[2.7.0], news_merge[2.7.0],
    po_merge[2.7.0], weave_fmt[2.7.0]
encoding: 'utf-8', fsenc: 'UTF-8', lang: 'en_GB.UTF-8'

*** Bazaar has encountered an internal error.  This probably indicates a
    bug in Bazaar.  You can help us fix it by filing a bug report at
        https://bugs.launchpad.net/bzr/+filebug
    including this traceback and a description of the problem.