This went out from the Official Star Wars Twitter in France:
“Together, we will destroy the Resistance and the last Jedi.”
The usage in the text specifically means “The final Jedi.” That clears that up for me. The text in English can be a bit ambiguous if it means a specific final Jedi or plurally. Luke Skywalker is the last Jedi in Star Wars: The Force Awakens in case there was any doubt.