The original paper is light on the countries of origins of the "participants"
"The experiments took place for 1 wk (January 11–18, 2012). Participants were randomly selected based on their User ID"
"such that no text was seen by the researchers. As such, it was consistent with Facebook’s Data Use Policy, to which all users agree prior to creating an account on Facebook, constituting informed consent for this research."
Not sure I would consider that informed consent. Supprised that the ethics comittee at Princeton bought it.
All to be found at http://www.pnas.org/content/111/24/8788.full