There is no difference for the second line. It was only posted as refference why the first line was wrong. There is no singular version for handcuffs in english language (afaik).
Edit: the same goes for german Floody and he also used the wrong timeform.
Code:
BUYHAND_MESSAGE = Sie kauften eine Handschelle.
Code:
BUYHAND_MESSAGE = Sie haben Handschellen gekauft.