How to mention paper that we withdrew and another paper under preparation in CV?
I would avoid mentioning the bad-quality conference and the withdrawal.  Mentioning it may send a negative message about your  planning habits, and your willingness to waste peoples' (reviewers') time due to those planning habits.

After re-submitting the paper, you can mention it in your CV if you clearly label it as "submitted". The other, unsubmitted paper can be mentioned as well, with the note "in progress" rather than "submitted".