Have you verified if the mod is enabled correctly (iow. the dll + exe + xml files are in the game root folder).
If you have updated the .py file with your preferred confidence level, and the testapp worked with that level, then I can't come up with a reason why it doesn't work in game. You could try removing the try: except: block in the InitializeScript-method and see if you get an exception (error) when the speech engine is loaded.
Like this:
Code:
def InitializeScript():
if SHSpeechEngine.IsSupported:
global speech
if speech == None:
speech = SHSpeechEngine("en-US")
speech.Confidence = 0.5
speech.OrderReceived += speech_OrderReceived
speech.Start()