Why do I get "Undefined index: mail en comment_form_validate()"? Is there a way to fix the notice I get? 


  Notice: Undefined index: mail en comment_form_validate()
  Notice: Undefined index: homepage en comment_form_validate() 


This appears in my message area with the errors for comments, only if I enable the development snapshot of the module to display errors or warnings (the configuration say I should turn this off in production), but I'm not sure if this is normal.  

Should I ignore this? The default comment module doesn't display this bug, with or without the  development snapshot settings working. Does anyone have a suggestion?
From your error messages it seems you are calling something like this

$form['field_name']['en'][0]['value']


Or something like that.  Which means the array key "en" is not available.  If you are not using languages, then I suggest using LANGUAGE_NONE as your key selector.

To prevent these types of messages you should perform an isset on the array element to make sure it exists before trying to retrieve a value from it.