Speech is unintelligible

[aasshhiisshh]

I am having this issue. While running, I installed all the required packages manually.
Unexpected error: <type 'exceptions.LookupError'> Speech is unintelligible

when this happen:
the syntax is "python main.py en"

Traceback (most recent call last):
File "main.py", line 59, in
mic.listen(handler, sample.mean(), sample.std())
File "/root/nltk/NatI/psw.py", line 70, in listen
l, data = self.inp.read()