There's a problem in that code in 1.2.6:

 def _warn_import_error(exc):
        [...]
        _warn("ImportError: %s" % msg)

The _warn() call will throw a unicode-decode-error when run on a french OS, for instance:
<type 'exceptions.UnicodeDecodeError'> 'ascii' codec can't decode byte 0xe9 in position 59: ordinal not in range(128)

Possibly a missing .encode('utf-8') on msg?