This is a French phrase that is not uncommon in English.
Pour encourager les autres is a quote from the French author Voltaire, referring to the excution of Admiral John Byng in the aftermath of the Battle of Minorca 1756.
The complete quote from Voltaire is Dans ce pays-ci, il est bon de tuer de temps en temps un amiral pour encourager les autres – "In this country, it is wise to kill an admiral from time to time to encourage the others."
This is of course a sarcastic statement, and is shortened to pour encourager les autres. It should be applied ironically to an action carried out in order to compel others to obey or submit.
More about the Battle of Minorca.
More about Voltaire.